Anemia

{{short description|Reduced ability of blood to carry oxygen}} {{Other uses}} {{Pp-move}} {{cs1 config|name-list-style=vanc}} {{Use American English|date=July 2024}} {{Use mdy dates|date=July 2024}} {{Infobox medical condition | name = Anemia | synonyms = Anaemia, erythrocytopenia | image = Iron deficiency anemia blood film.jpg | alt = Microsopic view with Giemsa staining of a blood smear with abnormally small and translucent red blood cells | caption = Blood smear showing iron-deficiency anemia, with small, pale red blood cells | field = Hematology | pronounce = {{IPAc-en|ə|ˈ|n|iː|m|i|ə}} | symptoms = Feeling tired, pale skin, weakness, shortness of breath, feeling faint<ref name="Janz-2013" >{{cite journal|vauthors = Janz TG, Johnson RL, Rubenstein SD|title = Anemia in the emergency department: evaluation and treatment | journal = Emergency Medicine Practice | volume = 15 | issue = 11 | pages = 1–15; quiz 15–16 | date = November 2013 | pmid = 24716235 |url= http://www.ebmedicine.net/topics.php?paction=showTopic&topic_id=385 }}</ref> | complications = | onset = | duration = | causes = Blood loss, decreased red blood cell production, increased red blood cell breakdown<ref name="Janz-2013" /> | risks = | diagnosis = Blood hemoglobin measurement<ref name="Janz-2013" /> | differential = | prevention = | treatment = | medication = | prognosis = | frequency = 1.92 billion / 24% (2021)<ref name="Gardner-2023a">{{cite journal | last1=Gardner | first1=William M | last2=Razo | first2=Christian | last3=McHugh | first3=Theresa A | last4=Hagins | first4=Hailey | last5=Vilchis-Tella | first5=Victor M | last6=Hennessy | first6=Conor | last7=Taylor | first7=Heather Jean | last8=Perumal | first8=Nandita | last9=Fuller | first9=Kia | last10=Cercy | first10=Kelly M | last11=Zoeckler | first11=Leo Zucker | last12=Chen | first12=Catherine S | last13=Lim | first13=Stephen S | last14=Aali | first14=Amirali | last15=Abate | first15=Kalkidan Hassen | last16=Abd-Elsalam | first16=Sherief | last17=Abdurehman | first17=Ame Mehadi | last18=Abebe | first18=Getachew | last19=Abidi | first19=Hassan | last20=Aboagye | first20=Richard Gyan | last21=Abolhassani | first21=Hassan | last22=Aboye | first22=Girma Beressa Aboye | last23=Abtew | first23=Yonas Derso | last24=Accrombessi | first24=Manfred Mario Kokou | last25=Adane | first25=Denberu Eshetie Adane | last26=Adane | first26=Tigist Demssew | last27=Addo | first27=Isaac Yeboah | last28=Adesina | first28=Miracle Ayomikun | last29=Adeyinka | first29=Daniel Adedayo | last30=Adnani | first30=Qorinah Estiningtyas Sakilah | title=Prevalence, years lived with disability, and trends in anaemia burden by severity and cause, 1990–2021: findings from the Global Burden of Disease Study 2021 | journal=The Lancet Haematology | volume=10 | issue=9 | year=2023 | issn=2352-3026 | doi=10.1016/s2352-3026(23)00160-6 | doi-access=free | pages=e713–e734 | pmid=37536353 |display-authors=1| pmc=10465717 | hdl=2164/22615 | hdl-access=free }}</ref> | deaths = }}

'''Anemia''' (also spelt '''anaemia''' in British English) is a blood disorder in which the blood has a reduced ability to carry oxygen. This can be due to a lower than normal number of red blood cells, a reduction in the amount of hemoglobin available for oxygen transport, or abnormalities in hemoglobin that impair its function.<ref name="EMed">{{cite web |title=Anemia: Practice Essentials, Pathophysiology, Etiology |url=https://emedicine.medscape.com/article/198475-overview |access-date=4 May 2025 |date=2 June 2025|last=Kreidieh|first=Firas|website=Medscape}}</ref><ref name="NHLBI-2022a">{{cite web |title=Anemia {{!}} NHLBI, NIH |url=https://www.nhlbi.nih.gov/health/anemia |website=www.nhlbi.nih.gov |access-date=8 February 2022}}</ref>

When anemia comes on slowly, the symptoms are often vague, such as tiredness, weakness, shortness of breath, headaches, and a reduced ability to exercise.<ref name="Janz-2013" /> When anemia is acute, symptoms may include confusion, feeling like one is going to pass out, loss of consciousness, and increased thirst.<ref name="Janz-2013" /> Anemia must be significant before a person becomes noticeably pale.<ref name="Janz-2013" /> Additional symptoms may occur depending on the underlying cause.<ref name="Janz-2013" /> Anemia can be temporary or long-term and can range from mild to severe.<ref name="Mayo-2022">{{cite web |title=Anemia – Symptoms and causes |url=https://www.mayoclinic.org/diseases-conditions/anemia/symptoms-causes/syc-20351360 |access-date=2022-04-01 |website=Mayo Clinic |language=en}}</ref>

Anemia can be caused by blood loss, decreased red blood cell production, and increased red blood cell breakdown.<ref name="Janz-2013" /> Causes of blood loss include menstruation, bleeding due to inflammation of the stomach or intestines, bleeding from surgery, serious injury, or blood donation.<ref name="Janz-2013" /> Causes of decreased production include iron deficiency, folate deficiency, vitamin B₁₂ deficiency, thalassemia and a number of bone marrow tumors.<ref name="Janz-2013" /> Causes of increased breakdown include genetic disorders such as sickle cell anemia, infections such as malaria, and certain autoimmune diseases like autoimmune hemolytic anemia.<ref name="Janz-2013" />

Anemia can also be classified based on the size of the red blood cells and amount of hemoglobin in each cell.<ref name="Janz-2013" /> If the cells are small, it is called microcytic anemia; if they are large, it is called macrocytic anemia; and if they are normal sized, it is called normocytic anemia.<ref name="Janz-2013" /> The diagnosis of anemia in men is based on a hemoglobin of less than 130&nbsp;g/L; in non-pregnant women, it is less than 120&nbsp;g/L, while in pregnant women it is less than 105–110.<ref>{{Cite web |date=2024 |title=Guideline on haemoglobin cutoffs to define anaemia in individuals and populations |url=https://iris.who.int/server/api/core/bitstreams/f9f74397-1440-478d-a63c-26f29a01552f/content |archive-url=http://web.archive.org/web/20260101164910/https://iris.who.int/server/api/core/bitstreams/f9f74397-1440-478d-a63c-26f29a01552f/content |archive-date=2026-01-01 |access-date=2026-01-27 |website=World Health Organization}}</ref><ref>{{Cite web |last=National Institute for Care and Health Excellence (NICE) |date=October 2025 |title=Anaemia - iron deficiency |url=https://cks.nice.org.uk/topics/anaemia-iron-deficiency/ |access-date=23 December 2025 |website=Clinical Knowledge Summaries}}</ref> Further testing is then required to determine the cause.<ref name="Janz-2013" /><ref name="Rhodes-2024">{{cite book |last1=Rhodes |first1=Carl E. |last2=Denault |first2=Deanna |last3=Varacallo |first3=Matthew |title=StatPearls |date=2024 |publisher=StatPearls Publishing |url=https://www.ncbi.nlm.nih.gov/books/NBK538336/ |chapter=Physiology, Oxygen Transport |pmid=30855920 }}</ref>

Treatment depends on the specific cause. Certain groups of individuals, such as pregnant women, can benefit from the use of iron pills for prevention.<ref name="Janz-2013" /><ref>{{cite journal | vauthors = Bhutta ZA, Das JK, Rizvi A, Gaffey MF, Walker N, Horton S, Webb P, Lartey A, Black RE | s2cid = 11748341 | title = Evidence-based interventions for improvement of maternal and child nutrition: what can be done and at what cost? | journal = Lancet | volume = 382 | issue = 9890 | pages = 452–477 | date = August 2013 | pmid = 23746776 | doi = 10.1016/S0140-6736(13)60996-4 | bibcode = 2013Lanc..382..452B }}</ref> Dietary supplementation, without determining the specific cause, is not recommended.<ref name="Janz-2013" /> The use of blood transfusions is typically based on a person's signs and symptoms.<ref name="Janz-2013" /> In those without symptoms, they are not recommended unless hemoglobin levels are less than 60 to 80&nbsp;g/L (6 to 8&nbsp;g/dL).<ref name="Janz-2013" /><ref name="Amir2013" /> These recommendations may also apply to some people with acute bleeding.<ref name="Janz-2013" /> Erythropoiesis-stimulating agents are only recommended in those with severe anemia.<ref name="Amir2013">{{cite journal | vauthors = Qaseem A, Humphrey LL, Fitterman N, Starkey M, Shekelle P | title = Treatment of anemia in patients with heart disease: a clinical practice guideline from the American College of Physicians | journal = Annals of Internal Medicine | volume = 159 | issue = 11 | pages = 770–779 | date = December 2013 | pmid = 24297193 | doi = 10.7326/0003-4819-159-11-201312030-00009 | s2cid = 4712203 | doi-access = }}</ref>

Anemia is the most common blood disorder, affecting about a fifth to a third of the global population.<ref name="Janz-2013" /><ref name="Vos-2016">{{cite journal |title=Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015 |journal=Lancet |volume=388 |issue=10053 |pages=1545–1602 |date=October 2016 |pmid=27733282 |pmc=5055577 |doi=10.1016/S0140-6736(16)31678-6 |url=|last1=Vos |first1=Theo |last2=Allen |first2=Christine |last3=Arora |first3=Megha |last4=Barber |first4=Ryan M. |last5=Bhutta |first5=Zulfiqar A. |last6=Brown |first6=Alexandria |last7=Carter |first7=Austin |last8=Casey |first8=Daniel C. |last9=Charlson |first9=Fiona J. |last10=Chen |first10=Alan Z. |last11=Coggeshall |first11=Megan |last12=Cornaby |first12=Leslie |last13=Dandona |first13=Lalit |last14=Dicker |first14=Daniel J. |last15=Dilegge |first15=Tina |last16=Erskine |first16=Holly E. |last17=Ferrari |first17=Alize J. |last18=Fitzmaurice |first18=Christina |last19=Fleming |first19=Tom |last20=Forouzanfar |first20=Mohammad H. |last21=Fullman |first21=Nancy |last22=Gething |first22=Peter W. |last23=Goldberg |first23=Ellen M. |last24=Graetz |first24=Nicholas |last25=Haagsma |first25=Juanita A. |last26=Hay |first26=Simon I. |last27=Johnson |first27=Catherine O. |last28=Kassebaum |first28=Nicholas J. |last29=Kawashima |first29=Toana |last30=Kemmer |first30=Laura |display-authors=1 }}</ref><ref>{{cite journal |last1=Peyrin-Biroulet |first1=Laurent |last2=Williet |first2=Nicolas |last3=Cacoub |first3=Patrice |title=Guidelines on the diagnosis and treatment of iron deficiency across indications: a systematic review |journal=The American Journal of Clinical Nutrition |date=1 December 2015 |volume=102 |issue=6 |pages=1585–1594 |doi=10.3945/ajcn.114.103366 |pmid=26561626 |doi-access=free }}</ref> Iron-deficiency anemia is the most common cause of anemia worldwide, and affects nearly one billion people.<ref name="Vos-2012">{{cite journal | vauthors = Vos T |display-authors=etal | title = Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010 | journal = Lancet | volume = 380 | issue = 9859 | pages = 2163–2196 | date = December 2012 | pmid = 23245607 |pmc=6350784 | doi = 10.1016/S0140-6736(12)61729-2 }}</ref> In 2013, anemia due to iron deficiency resulted in about 183,000 deaths – down from 213,000 deaths in 1990.<ref name="GBD2013">{{cite journal |title=Global, regional, and national age-sex specific all-cause and cause-specific mortality for 240 causes of death, 1990–2013: a systematic analysis for the Global Burden of Disease Study 2013 |journal=Lancet |volume=385 |issue=9963 |pages=117–71 |date=January 2015 |pmid=25530442 |pmc=4340604 |doi=10.1016/S0140-6736(14)61682-2 |url=|author1=((GBD 2013 Mortality Causes of Death Collaborators))}}</ref> This condition is most prevalent in children<ref>{{cite web|title=WHO Global Anaemia estimates, 2021 Edition |url=https://www.who.int/data/gho/data/themes/topics/anaemia_in_women_and_children|work=World Health Organization|access-date=27 February 2022}}</ref><ref>{{cite journal |last1=Islam |first1=Md Azmir Ibne |title=Modeling the impact of campaign program on the prevalence of anemia in children under five: Anemia model |journal=Journal of Mathematical Analysis and Modeling |date=6 December 2021 |volume=2 |issue=3 |pages=29–40 |doi=10.48185/jmam.v2i3.362 |url=https://www.sabapub.com/index.php/jmam/article/view/362 |language=en |issn=2709-5924|doi-access=free }}</ref> with also an above average prevalence in elderly<ref name="Janz-2013" /> and women of reproductive age (especially during pregnancy).<ref name="Vos-2012" /> Women aged 15 to 49 years experienced an increase in the global prevalence from 27.6% to 30.7% between 2012 to 2023 with either no improvement or an increase in prevalence in nearly all regions.<ref name="Food Security-2025a">{{Cite book |last1=FAO |url=https://openknowledge.fao.org/handle/20.500.14283/cd6008en |title=The State of Food Security and Nutrition in the World 2025 |last2=IFAD |last3=UNICEF |last4=WFP |last5=WHO |date=2025 |publisher=FAO ; IFAD ; UNICEF ; WFP ; WHO |isbn=978-92-5-139937-8 |language=English |doi=10.4060/cd6008en}}</ref> Anemia is one of the six WHO global nutrition targets for 2025 and for diet-related global targets endorsed by World Health Assembly in 2012 and 2013. Efforts to reach global targets contribute to reaching Sustainable Development Goals (SDGs),<ref>{{cite web|title=WHO {{!}} Interventions by global target|url=https://www.who.int/elena/global-targets/en/ |archive-url=https://web.archive.org/web/20160814083405/http://www.who.int/elena/global-targets/en/ |archive-date=August 14, 2016 |website=www.who.int |publisher=World Health Organization}}</ref> with anemia as one of the targets in SDG 2 for achieving zero world hunger.<ref>{{cite web|date=14 June 2016|publisher=Devex|title=The case for action on anemia|url=https://www.devex.com/news/sponsored/the-case-for-action-on-anemia-leave-no-one-behind-88283}}</ref>{{TOC limit|3}}

==Signs and symptoms== thumb|upright=1.2|Main symptoms that may appear in anemia<ref name="eMedicineHealth">{{Cite web |title=Anemia Types, Treatment, Symptoms, Signs, Causes & Iron Deficiency |url=https://www.emedicinehealth.com/anemia/article_em.htm |access-date=2026-01-09 |website=eMedicineHealth |language=en}}</ref>|alt=Chart listing symptoms of anemia and locating them to areas of the body. Eyes: yellowing. Skin: paleness, coldness, yellowing. Respiratory: shortness of breath. Muscular: weakness. Intestinal: changed stool color. Central: fatigue, dizziness; in severe cases fainting. Blood vessels: low blood pressure. Heart: palpitations, rapid heart rate; in severe cases chest pain, angina, heart attack. Spleen: enlargement. Symptoms of anemia can come on quickly or slowly.<ref name="NHLBI-2022b">{{cite web |date=2022-03-24 |title=What Are Symptoms of Anemia? |url=https://www.nhlbi.nih.gov/health/anemia/symptoms |access-date=2022-06-26 |website=National Heart, Lung, and Blood Institute.}}</ref> If the anemia develops slowly (chronic), the body may adapt and compensate for this change up to a point. In this case, no symptoms may appear until the anemia becomes more severe.<ref name="eMedicineHealth" /><ref name="Am Soc Hematology-2026">{{cite web |title=Anemia |url=https://www.hematology.org:443/education/patients/anemia |access-date=2026-01-09 |website=American Society of Hematology |language=en}}</ref> General symptoms of mild anemia can include feeling tired, weak, dizziness, headaches, shortness of breath, and pale or yellowish skin.<ref name="Am Soc Hematology-2026" /><ref>{{Cite web |title=Anemia |url=https://www.yalemedicine.org/conditions/anemia |access-date=2026-01-09 |website=Yale Medicine |language=en}}</ref>

Acute anemia, often caused by blood loss (hemorrhagic shock) has more severe symptoms, including rapid heartbeat, low blood pressure,and confusion.<ref name="Killeen-2026">{{Citation |last1=Killeen |first1=Robert B. |title=Acute Anemia |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK537232/ |access-date=2026-03-21 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30725917 |last2=Kaur |first2=Anahat |last3=Afzal |first3=Muriam}}</ref>

The body may compensate for the lack of oxygen-carrying capability of the blood by increasing cardiac output. Symptoms related to this may include palpitations, angina (if pre-existing heart disease is present), difficulty walking, and symptoms of heart failure.<ref>{{cite journal |last1=De Franceschi |first1=Lucia |last2=Iolascon |first2=Achille |last3=Taher |first3=Ali |last4=Cappellini |first4=Maria Domenica |title=Clinical management of iron deficiency anemia in adults: Systemic review on advances in diagnosis and treatment |journal=European Journal of Internal Medicine |date=July 2017 |volume=42 |pages=16–23 |doi=10.1016/j.ejim.2017.04.018 |pmid=28528999 }}</ref> In severe anemia, there may be signs of a hyperdynamic circulation: tachycardia (a fast heart rate), bounding pulse, flow murmurs, and cardiac ventricular hypertrophy (enlargement).<ref name="Killeen-2026" />

thumb|upright=1.2|The hand of a person with severe anemia (on the left, with ring) compared to the hand of a person without anemia (on the right)|alt=Image of two light-skinned hands. Left hand appears pale and yellow and wearing a ring on the ring finger. Right hand appears pinkish.|leftChronic anemia in infants may result in poor growth and impaired neurological development.<ref>{{Cite journal |last=Gallagher |first=Patrick G. |date=2022-08-11 |title=Anemia in the pediatric patient |url=https://ashpublications.org/blood/article/140/6/571/484178/Anemia-in-the-pediatric-patient |journal=Blood |language=en |volume=140 |issue=6 |pages=571–593 |doi=10.1182/blood.2020006479 |issn=0006-4971 |pmc=9373018 |pmid=35213686}}</ref>

Pallor resulting from severe anemia may be visible in the hand palms and fingernails beds, although it may be difficult to detect in dark toned skin. Other locations to detect pallor are the inner lining of the lower eyelid and the tongue.<ref>{{Cite journal |last1=Ersianti |first1=Yuninda Loviana |last2=Susanah |first2=Susi |last3=Winarno |first3=Gatot Nyarumenteng Adhipurnawan |last4=Susiarno |first4=Hadi |last5=Herman |first5=Herry |last6=Krisnadi |first6=Sofie Rifayani |date=2026 |title=Analysis of Pallor Examination for the Identification of Anemia Among Pregnant Women: A Scoping Review |journal=International Journal of Women's Health |language=English |volume=18 |pages=1–12 |doi=10.2147/IJWH.S550863 |doi-access=free |pmid=41835843 |pmc=12983172 }}</ref><ref name="WHO-2025b">{{Cite web |title=Anaemia |url=https://www.who.int/news-room/fact-sheets/detail/anaemia |access-date=2026-01-09 |website=World Health Organization |language=en|date=10 February 2025}}</ref><ref>{{Cite web |title=Identifying AEFI in diverse skin colour |url=https://mvec.mcri.edu.au/references/identifying-aefi-in-diverse-skin-colour/ |access-date=2026-03-21 |website=The Melbourne Vaccine Education Centre (MVEC) |language=en-AU}}</ref>

Other symptoms associated with anemia depend on the underlying cause of the disorder; for example -

* Chronic iron-deficiency anemia may be associated with symptoms that can include spoon-shaped nails, sore or abnormally smooth tongue, hair loss, or pica (the desire to eat things which are not food, such as ice or earth).<ref>{{Cite web |date=21 February 2025 |title=Iron deficiency anaemia symptoms and treatments |url=https://www.nhsinform.scot/illnesses-and-conditions/nutritional/iron-deficiency-anaemia/ |access-date=2026-03-27 |website=NHS inform |language=en-GB}}</ref> * Anemia caused by vitamin B₁₂ deficiency may be associated with psychological problems such as anxiety and confusion, memory loss, and depression.<ref>{{Cite web |date=20 February 2023 |title=Vitamin B12 or folate deficiency anaemia |url=https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/ |access-date=2026-03-27 |website=National Health Service |language=en}}</ref> ==Diagnosis== [[File:Iron deficiency anemia.jpg|thumb|Peripheral blood smear microscopy of a patient with iron-deficiency anemia|alt=Microscopic view with H&E stain of a blood smear with abnormally small, pale red blood cells]] thumb|A Giemsa-stained blood film from a person with iron-deficiency anemia. This person also had hemoglobin Kenya.|alt=Microscopic view with Giemsa stain of a blood smear with abnormally small, pale red blood cells

===Definitions=== There are several definitions of anemia.<ref name="Beutler-2006">{{cite journal | vauthors = Beutler E, Waalen J | title = The definition of anemia: what is the lower limit of normal of the blood hemoglobin concentration? | journal = Blood | volume = 107 | issue = 5 | pages = 1747–1750 | date = March 2006 | pmid = 16189263 | pmc = 1895695 | doi = 10.1182/blood-2005-07-3046 }}</ref> A strict but broad definition is an absolute decrease in red blood cell mass,<ref>{{EMedicine|article|198475|Anemia}}</ref> however, a broader definition is a lowered ability of the blood to carry oxygen.<ref name="Rodak-2007">{{cite book|last=Rodak|first=Bernadette F.|url=https://books.google.com/books?id=6sfacydDNsUC&pg=PA220|title=Hematology: Clinical Principles and Applications|date=2007|publisher=Saunders|isbn=978-1-4160-3006-5|edition=3rd|location=Philadelphia|page=220|archive-url=https://web.archive.org/web/20160425061405/https://books.google.com/books?id=6sfacydDNsUC&pg=PA220|archive-date=2016-04-25|url-status=live}}</ref> An operational definition is a decrease in whole-blood hemoglobin concentration of more than 2 standard deviations below the mean of an age- and sex-matched reference range.<ref name="PDMS2">{{cite book | first1 = Albert J. | last1 = Pomeranz | first2 = Svapna | last2 = Sabnis | first3 = Sharon | last3 = Busey | first4 = Robert M. | last4 = Kliegman |year=2016 |title=Pediatric Decision-Making Strategies |edition=2nd |publisher=Elsevier |isbn=978-0-323-29854-4 }}</ref> {| class="wikitable" |+ World Health Organization Hemoglobin thresholds used to define anemia<ref name="WHO-Guidelines-2024">{{Cite book |last=World Health Organization |date=2024 |title=Guideline on haemoglobin cutoffs to define anaemia in individuals and populations |url=https://iris.who.int/server/api/core/bitstreams/f9f74397-1440-478d-a63c-26f29a01552f/content |access-date=2025-12-23 |page=xi |publisher=World Health Organization |language=en |isbn=978-92-4-008854-2}}</ref> |- ! Age or gender group ! Hb threshold (g/L) |- | Children (0.5–2 yrs) | 105 |- | Children (2–5 yrs) | 110 |- | Children (5–12 yrs) | 115 |- |Teens (12–15 yrs) |120 |- | Non-pregnant women (>15yrs) | 120 |- | Pregnant girls and women | 105–110 |- | Men (>15yrs) | 130 |}

==== Etymology ==== The name is derived {{ety|grc|''ἀν''- (an-)|not||"αἷμᾰ" (haîmă)|blood}}.<ref>{{cite web|title=anaemia|url=http://dictionary.reference.com/browse/anaemia|website=Dictionary.com|access-date=7 July 2014|url-status = live|archive-url=https://web.archive.org/web/20140714223241/http://dictionary.reference.com/browse/anaemia|archive-date=14 July 2014}}</ref> A related word, ''ischemia'', derives from the Greek from ῐ̓́σχω (''ĭ́skhō'', "stop") and αἷμᾰ (''haîmă'', "blood"); the roots of the both words refer to the basic idea of "lack of blood", but the meaning is significantly different. ''Anemia'' implies widespread effects from blood that either is too scarce (e.g., blood loss) or is dysfunctional in its oxygen-supplying ability (due to whatever type of hemoglobin or erythrocyte problem). ''Ischemia'' is a restriction in blood supply to any tissue, muscle, or organ of the body, causing a shortage of oxygen that is needed to keep tissues alive, as may occur for example in a stroke.<ref>Merck & Co. [http://www.merckmanuals.com/home/heart_and_blood_vessel_disorders/peripheral_arterial_disease/occlusive_peripheral_arterial_disease.html#v722187 Occlusive Peripheral Arterial Disease], The Merck Manual Home Health Handbook website, revised and updated March 2010. Retrieved March 4, 2012.</ref><ref>{{Cite web |title=Chronic Limb-Threatening Ischemia (CLTI) – Vascular Cures|url=https://vascularcures.org/chronic-limb-threatening-ischemia-clti/|access-date=2021-10-27|language=en-US|archive-date=2021-10-29|archive-url=https://web.archive.org/web/20211029044416/https://vascularcures.org/chronic-limb-threatening-ischemia-clti/}}</ref><ref>{{cite journal |last1=Bellotto |first1=Fabio |last2=Cati |first2=Arianna |title=Anemia ed ischemia miocardica: relazioni ed interferenze |trans-title=Anemia and myocardial ischemia: relationships and interferences |language=it |journal=Recenti Progressi in Medicina |date=March 2006 |volume=97 |issue=3 |pages=153–164 |doi=10.1701/121.1312 |pmid=16700423 }}</ref> ===Testing=== Anemia is typically diagnosed on a complete blood count from a blood sample. An automated hematology analyzer measures the hemoglobin level, hematocrit (% volume of RBCs in the blood), the size of the RBCs,<ref>{{Cite journal |last=Chhabra |first=Gaurav |date=2017-12-01 |title=Automated hematology analyzers: Recent trends and applications |journal=Journal of Laboratory Physicians |language=en |volume=10 |issue=1 |pages=15–16 |doi=10.4103/JLP.JLP_124_17 |doi-access=free |issn=0974-2727 |pmc=5784285 |pmid=29403197}}</ref> and counts of white blood cells and platelets.

Further tests will be needed to determine the underlying cause; these may include (not a complete list):<ref>{{cite web |title=Anemia|url=https://www.radiologyinfo.org/en/info/anemia|access-date=2021-10-11|website=Radiologyinfo.org|language=en}}</ref><ref name="Freeman-2026a">{{Citation |last=Freeman|first=Andrew M.|title=Anemia Screening|date=2026|work=StatPearls|url=http://www.ncbi.nlm.nih.gov/books/NBK499905/|access-date=2026-03-30|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=29763080|last2=Zubair|first2=Muhammad}}</ref>

* A count of reticulocytes (immature RBCs), which measures the capacity of the bone marrow to produce new RBCs.<ref>{{Cite web |title=Reticulocyte Count: Testing, Purpose & Results|url=https://my.clevelandclinic.org/health/diagnostics/22787-reticulocyte-count|archive-url=http://web.archive.org/web/20260207050533/https://my.clevelandclinic.org/health/diagnostics/22787-reticulocyte-count|archive-date=2026-02-07|access-date=2026-03-30|website=Cleveland Clinic|language=en}}</ref> * Iron profile, to establish if there is underlying iron deficiency (the most common cause of anemia).<ref name="Freeman-2026b">{{Citation |last=Freeman|first=Andrew M.|title=Anemia Screening|date=2026|work=StatPearls|url=http://www.ncbi.nlm.nih.gov/books/NBK499905/|access-date=2026-03-30|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=29763080|last2=Zubair|first2=Muhammad}}</ref> * Family history and genetic testing, to establish if there is an inherited disorder (the second most common cause).<ref name="Freeman-2026b" /> * Peripheral blood smear - a small blood sample is examined under a microscope to check the size and shape of RBCs. Among other things, this should detect malaria parasites, which are globally the third most common cause.<ref>{{Cite web |last=Al Hadidi|first=Samer|date=17 August 2021|title=Blood Smear: The Fifth Vital Sign in Hematology - Hematology.org|url=https://www.hematology.org/education/trainees/fellows/hematopoiesis/2021/blood-smear|access-date=2026-03-30|website=American Society of Hematology|language=en}}</ref><ref>{{Cite web |date=January 2024|title=How should I assess a person with suspected malaria?|url=https://cks.nice.org.uk/topics/malaria/diagnosis/assessment/|access-date=30 March 2026|website=National Institute for Health and Care Excellence}}</ref> * Serum creatinine, to check if poor kidney function underlies the anemia.<ref>{{Cite web |date=2019-03-28|title=Anaemia|url=https://www.kidney.org.uk/anaemia|access-date=2026-03-30|website=National Kidney Federation|language=en}}</ref> ==Causes== thumb|Figure shows normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a normal red blood cell with normal hemoglobin.<ref>{{cite web |title=Sickle Cell Disease |url=https://www.nhlbi.nih.gov/health/sickle-cell-disease |website=National Heart, Lung, and Blood Institute |date=22 July 2022 }}</ref>|alt=See caption In humans, mature red blood cells (RBCs) are flexible biconcave disks, lacking cell nucleus and organelles. The process by which new RBCs are produced is termed erythropoiesis; committed stem cells in the red bone marrow of large bones take 7 days to mature into red blood cells. Between 2 and 3 million new RBCs are produced per second in human adults.<ref>{{Citation |last=Dean|first=Laura|title=Blood and the cells it contains|date=2005|work=Blood Groups and Red Cell Antigens [Internet]|url=https://www.ncbi.nlm.nih.gov/books/NBK2263/|access-date=2026-03-16|publisher=National Center for Biotechnology Information (US)|language=en}}</ref> The functional lifetime of a RBC is about 100–120 days, during which time the cells are continually moving within the blood circulation.<ref>{{cite journal |vauthors=Higgins JM|date=March 2015|title=Red blood cell population dynamics|journal=Clinics in Laboratory Medicine|volume=35|issue=1|pages=43–57|doi=10.1016/j.cll.2014.10.002|pmc=4717490|pmid=25676371}}</ref> The aging RBC undergoes changes in its plasma membrane, making it susceptible to recognition by macrophages and subsequent breakdown in the spleen, thus removing old and defective cells and continually purging the blood.<ref>Lutz HU, Bogdanova A. Mechanisms tagging senescent red blood cells for clearance in healthy humans. Front Physiol. 2013;4:387</ref> This process is termed eryptosis; much of the resulting breakdown products are recirculated in the body.<ref>{{cite journal |vauthors=Föller M, Huber SM, Lang F|date=October 2008|title=Erythrocyte programmed cell death|journal=IUBMB Life|volume=60|issue=10|pages=661–668|doi=10.1002/iub.106|pmid=18720418|s2cid=41603762|doi-access=free}}</ref> RBC breakdown by eryptosis normally occurs at the same rate as production by erythropoiesis, thus maintaining a balanced RBC population in the circulation.<ref name="Lang-2012">{{cite journal |vauthors=Lang F, Lang E, Föller M|date=October 2012|title=Physiology and pathophysiology of eryptosis|journal=Transfusion Medicine and Hemotherapy|volume=39|issue=5|pages=308–314|doi=10.1159/000342534|pmc=3678267|pmid=23801921}}</ref>

The causes of anemia may be classified as impaired red blood cell (RBC) production, increased RBC destruction (hemolytic anemia), blood loss, and fluid overload (hypervolemia).<ref>{{Cite web |last=Amilia |first=Alifrangis |date=December 2022 |title=Anaemia: Symptoms, causes and treatment {{!}} Bupa UK |url=https://www.bupa.co.uk/health-information/heart-blood-circulation/anaemia |access-date=2026-03-19 |website=www.bupa.co.uk |language=en-GB}}</ref> Globally, the most common underlying cause of anemia is dietary iron deficiency, followed by the inherited conditions thalassaemia and sickle cell trait, and infectious disease (principally malaria).<ref name="WHO-2025b" />

===Impaired production=== * Disturbance of proliferation and differentiation of stem cells ** Pure red cell aplasia<ref name="Mitchell-2007">Table 12-1 in: {{cite book | last1 = Mitchell | first1 = Richard Sheppard | last2 = Kumar | first2 = Vinay | last3 = Abbas | first3 = Abul K. | last4 = Fausto | first4 = Nelson | title = Robbins Basic Pathology | publisher = Saunders | location=Philadelphia |year= 2007|isbn=978-1-4160-2973-1 | edition = 8th}}</ref> ** Aplastic anemia<ref name="Mitchell-2007" /> affects all kinds of blood cells. Fanconi anemia is a hereditary disorder or defect featuring aplastic anemia and various other abnormalities, including malformation of the extremities.<ref>{{Citation |last1=Bhandari |first1=Jenish |title=Fanconi Anemia |date=2024-06-19 |work=StatPearls [Internet] |url=https://www.ncbi.nlm.nih.gov/sites/books/NBK559133/ |access-date=2026-01-08 |publisher=StatPearls Publishing |language=en |pmid=32644559 |last2=Thada |first2=Pawan K. |last3=Killeen |first3=Robert B. |last4=Puckett |first4=Yana}}</ref> ** Anemia of kidney failure<ref name="Mitchell-2007" /> due to insufficient production of the hormone erythropoietin ** Anemia of endocrine disease<ref>{{cite book|last1=Gregg|first1=XT|last2=Prchal|first2=JT|title=Williams Hermatology|date=2007|publisher=McGraw-Hill|chapter=Anemia of Endocrine Disorders}}</ref> * Disturbance of proliferation and maturation of erythroblasts ** Pernicious anemia is a form of megaloblastic anemia due to vitamin B₁₂ deficiency.<ref name="Mitchell-2007" /> ** Anemia of folate deficiency, as with vitamin B₁₂, causes megaloblastic anemia.<ref name="Mitchell-2007" /> ** Anemia of prematurity, by diminished erythropoietin response to declining hematocrit levels, combined with blood loss from laboratory testing, generally occurs in premature infants at two to six weeks of age.<ref>{{Cite web |last=Garcia-Prats |first=Joseph A |date=23 June 2025 |title=Anemia of prematurity (AOP) |url=https://www.uptodate.com/contents/anemia-of-prematurity-aop |access-date=2026-04-12 |website=Uptodate Inc.}}</ref> ** Iron-deficiency anemia, resulting in deficient heme synthesis.<ref name="Mitchell-2007" /> Globally, this is the most common type of anemia; it may be caused by poor diet (common in poor communities),<ref name="WHO-2025a">{{Cite web |date=10 February 2025 |title=Anaemia |url=https://www.who.int/news-room/fact-sheets/detail/anaemia |access-date=2026-04-17 |website=World Health Organization |language=en}}</ref> blood loss, or poor absorption of iron from food.<ref name="NHLBI-2022c">{{cite web|title=What Is Anemia?|website=National Heart, Lung, and Blood Institute (NHLBI)|date=24 March 2022|url=https://www.nhlbi.nih.gov/health/anemia|access-date=8 March 2025|archive-date=13 June 2022|archive-url=https://web.archive.org/web/20220613171724/https://www.nhlbi.nih.gov/health/anemia|url-status=live}}</ref> Sources of blood loss can include heavy periods, childbirth, uterine fibroids, stomach ulcers, colon cancer, and urinary tract bleeding.<ref name="NHLBI-2025">{{cite web|title=Causes and Risk Factors|website=National Heart, Lung, and Blood Institute (NHLBI)|date=24 March 2022|url=https://www.nhlbi.nih.gov/health/anemia/causes|access-date=8 March 2025}}</ref> Poor absorption of iron from food may occur as a result of an intestinal disorder such as inflammatory bowel disease or celiac disease, or surgery such as a gastric bypass.<ref name="NHLBI-2025" /> In low income communities with poor diet, parasitic worms, malaria, and HIV/AIDS increase the risk of iron deficiency anemia.<ref name="WHO-2025a" /> ** Thalassemias, causing deficient globin synthesis<ref name="Mitchell-2007" /> ** Congenital dyserythropoietic anemias, causing ineffective erythropoiesis.<ref name="MedlinePlus-CDA">{{Cite web |title=Congenital dyserythropoietic anemia: MedlinePlus Genetics|url=https://medlineplus.gov/genetics/condition/congenital-dyserythropoietic-anemia/|access-date=2025-10-08|website=National Library of Medicine|language=en}}</ref> ** Anemia of kidney failure.<ref name="Mitchell-2007" /> * Other mechanisms of impaired RBC production ** Myelophthisic anemia or myelophthisis is a severe type of anemia resulting from the replacement of bone marrow by other materials, such as malignant tumors, fibrosis, or granulomas.<ref name="Mitchell-2007" /> The term ''Leukoerythroblastic'' is applied to a typical blood smear showing immature and abnormal erythrocytes.<ref>{{Cite web |date=10 January 2022 |title=Myelophthisic Anemia Workup: Approach Considerations, Leukoerythroblastic Picture, Histologic Findings |url=https://emedicine.medscape.com/article/204647-workup#c7 |access-date=2026-04-15 |website=MedScape}}</ref> ** Myelodysplastic syndrome<ref name="Mitchell-2007" />

* Anemia of chronic disease. ** Chronic inflammation can disrupt iron handling, limiting its availability for red blood cell formation.<ref name="Mitchell-2007" /> In chronic inflammation, the liver produces high levels of hepcidin, a hormone which regulates iron metabolism.<ref name="Ganz_2003">{{cite journal |vauthors=Ganz T|title=Hepcidin, a key regulator of iron metabolism and mediator of anemia of inflammation|journal=Blood|volume=102|issue=3|pages=783–788|date=August 2003|pmid=12663437|doi=10.1182/blood-2003-03-0672|doi-access=free}}</ref> This leads to high ferritin levels and low transferrin saturation, a pattern known as "functional iron deficiency." In this condition, iron availability is restricted even when total body iron stores are adequate, contributing to anemia common in inflammatory bowel diseases and chronic infections.<ref name="Dugdale-2001">{{Cite journal|title=ANEMIA|url=https://www.sciencedirect.com/science/article/pii/S0889854505702060|journal=Obstetrics and Gynecology Clinics of North America|date=2001-06-01|issn=0889-8545|pages=363–382|volume=28|issue=2|doi=10.1016/S0889-8545(05)70206-0|first=Marion|last=Dugdale |pmid=11430182 |url-access=subscription}}</ref> This mechanism is commonly seen in older hospitalized patients with long-standing illnesses such as infections, heart failure or autoimmune conditions.<ref name="Randi-2020">{{Cite journal|title=Prevalence and Causes of Anemia in Hospitalized Patients: Impact on Diseases Outcome|journal=Journal of Clinical Medicine|date=2020-03-30|issn=2077-0383|pmc=7230611|pmid=32235484|page=950|volume=9|issue=4|doi=10.3390/jcm9040950|language=en|first1=Maria Luigia|last1=Randi|first2=Irene|last2=Bertozzi|first3=Claudia|last3=Santarossa|first4=Elisabetta|last4=Cosi|first5=Fabrizio|last5=Lucente|first6=Giulia|last6=Bogoni|first7=Giacomo|last7=Biagetti|first8=Fabrizio|last8=Fabris |doi-access=free }}</ref> ** Intestinal inflammation, which may be caused by: ''Helicobacter pylori'' infection.<ref name="Stein-2016">{{cite journal | vauthors = Stein J, Connor S, Virgin G, Ong DE, Pereyra L | title = Anemia and iron deficiency in gastrointestinal and liver conditions | journal = World Journal of Gastroenterology | volume = 22 | issue = 35 | pages = 7908–7925 | date = September 2016 | pmid = 27672287 | pmc = 5028806 | doi = 10.3748/wjg.v22.i35.7908 | type = Review | doi-access = free }}</ref>, gluten-related disorders such as untreated celiac disease<ref name="Leffler-2015">{{cite journal |last1=Leffler |first1=Daniel A. |last2=Green |first2=Peter H. R. |last3=Fasano |first3=Alessio |title=Extraintestinal manifestations of coeliac disease |journal=Nature Reviews Gastroenterology & Hepatology |date=October 2015 |volume=12 |issue=10 |pages=561–571 |doi=10.1038/nrgastro.2015.131 |pmid=26260366 |s2cid=15561525 }}</ref><ref name="Stein-2016" /> and non-celiac gluten sensitivity;<ref name="Catassi-2013">{{cite journal | vauthors = Catassi C, Bai JC, Bonaz B, Bouma G, Calabrò A, Carroccio A, Castillejo G, Ciacci C, Cristofori F, Dolinsek J, Francavilla R, Elli L, Green P, Holtmeier W, Koehler P, Koletzko S, Meinhold C, Sanders D, Schumann M, Schuppan D, Ullrich R, Vécsei A, Volta U, Zevallos V, Sapone A, Fasano A | title = Non-Celiac Gluten sensitivity: the new frontier of gluten related disorders | journal = Nutrients | volume = 5 | issue = 10 | pages = 3839–3853 | date = September 2013 | pmid = 24077239 | pmc = 3820047 | doi = 10.3390/nu5103839 | type = Review | doi-access = free }}</ref> or Inflammatory bowel disease.<ref name="Lomer-2011">{{cite journal | vauthors = Lomer MC | title = Dietary and nutritional considerations for inflammatory bowel disease | journal = The Proceedings of the Nutrition Society | volume = 70 | issue = 3 | pages = 329–335 | date = August 2011 | pmid = 21450124 | doi = 10.1017/S0029665111000097 | type = Review | doi-access = free }}</ref><ref name="Gerasimidis-2011">{{cite journal | vauthors = Gerasimidis K, McGrogan P, Edwards CA | title = The aetiology and impact of malnutrition in paediatric inflammatory bowel disease | journal = Journal of Human Nutrition and Dietetics | volume = 24 | issue = 4 | pages = 313–326 | date = August 2011 | pmid = 21564345 | doi = 10.1111/j.1365-277X.2011.01171.x | type = Review | doi-access = free }}</ref>

===Increased destruction=== {{Further|Hemolytic anemia}} Anemias of increased red blood cell destruction are generally classified as hemolytic anemias. These types generally feature jaundice, and elevated levels of lactate dehydrogenase.<ref>{{cite web |url= https://www.lecturio.com/concepts/anemia-overview/ | title= Overview of hemolytic anemias in children | last1= Despotovic | first1= J | last2= Mahoney | first2= D | last3= Armsby | first3= C | publisher= UpToDate |date= 2021 |website= The Lecturio Medical Concept Library |access-date= 28 June 2021}}</ref><ref>{{cite book|author=Capriotti, Theresa|title=Pathophysiology: introductory concepts and clinical perspectives|author2=Frizzell, Joan Parker|year=2016|isbn=978-0-8036-1571-7|location=Philadelphia |publisher=F.A. Davis Company |oclc=900626405}}</ref> * Intrinsic (intracorpuscular) abnormalities<ref name="Mitchell-2007" /> cause premature destruction. All of these, except paroxysmal nocturnal hemoglobinuria, are hereditary genetic disorders.<ref name="Mitchell-2007a">{{cite book | last1 = Mitchell | first1 = Richard Sheppard | last2 = Kumar | first2 = Vinay | last3 = Abbas | first3 = Abul K. | last4 = Fausto | first4 = Nelson | title = Robbins Basic Pathology | publisher = Saunders | location=Philadelphia |page= 432 |isbn=978-1-4160-2973-1 | edition = 8th | year = 2007 }}</ref> ** Hereditary spherocytosis<ref name="Mitchell-2007" /> is a hereditary defect that results in defects in the RBC cell membrane, causing the erythrocytes to be sequestered and destroyed by the spleen.<ref>{{Citation |last=Zamora |first=Edgar A. |title=Hereditary Spherocytosis |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK539797/ |access-date=2026-04-19 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30969619 |last2=Schaefer |first2=Catherine A.}}</ref> ** Hereditary elliptocytosis<ref name="Mitchell-2007" /> is another defect in membrane skeleton proteins. ** Abetalipoproteinemia,<ref name="Mitchell-2007" /> causing defects in membrane lipids.<ref>{{Citation |last=Junaid |first=Syeda Zeenat S. |title=Abetalipoproteinemia |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK513355/ |access-date=2026-04-19 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=30020727 |last2=Patel |first2=Krunal}}</ref> ** Enzyme deficiencies *** Pyruvate kinase and hexokinase deficiencies,<ref name="Mitchell-2007" /> causing defect glycolysis.<ref>{{cite journal |vauthors=Grace RF, Zanella A, Neufeld EJ, Morton DH, Eber S, Yaish H, Glader B|title=Erythrocyte pyruvate kinase deficiency: 2015 status report|journal=American Journal of Hematology|volume=90|issue=9|pages=825–30|date=September 2015|pmid=26087744|doi=10.1002/ajh.24088|pmc=5053227}}</ref> *** Glucose-6-phosphate dehydrogenase deficiency (G6PDD) and glutathione synthetase deficiency,<ref name="Mitchell-2007" /> causing increased oxidative stress.<ref name="Frank-2005a">{{Cite journal |last=Frank|first=Jennifer E.|date=2005-10-01|title=Diagnosis and Management of G6PD Deficiency|url=https://www.aafp.org/afp/2005/1001/p1277.html|journal=American Family Physician|volume=72|issue=7|pages=1277–1282|pmid=16225031|issn=0002-838X}}</ref> ** Hemoglobinopathies *** Sickle cell anemia<ref name="Mitchell-2007" /> *** Hemoglobinopathies causing unstable hemoglobins<ref name="Mitchell-2007" /> ** Paroxysmal nocturnal hemoglobinuria<ref name="Mitchell-2007" /> * Extrinsic (extracorpuscular) abnormalities ** Antibody-mediated *** Warm autoimmune hemolytic anemia is caused by an autoimmune attack against red blood cells, primarily by IgG. It is the most common of the autoimmune hemolytic diseases.<ref name="Cotran-2005">{{cite book | last1 = Cotran | first1 = Ramzi S. | last2 = Kumar | first2 = Vinay | last3 = Fausto | first3 = Nelson | last4 = Robbins | first4 = Stanley L. | last5 = Abbas | first5 = Abul K. | title=Robbins and Cotran pathologic basis of disease |publisher=Elsevier Saunders |location=St. Louis, Mo |year=2005 |page=637 |isbn=978-0-7216-0187-8 }}</ref> It can be idiopathic, that is, without any known cause, drug-associated or secondary to another disease such as systemic lupus erythematosus, or a malignancy, such as chronic lymphocytic leukemia.<ref name="Jenkins">[http://www.trcc.org/blood/10b_autoimmune.pdf "Autoimmune Hemolytic Anemia (AIHA)"] By J.L. Jenkins. The Regional Cancer Center. 2001 {{webarchive |url=https://web.archive.org/web/20091007084816/http://www.trcc.org/blood/10b_autoimmune.pdf |date=October 7, 2009 }}</ref> *** Cold agglutinin hemolytic anemia is primarily mediated by IgM. It can be idiopathic or result from an underlying condition.<ref name="Berentsen-2007">{{cite journal | vauthors = Berentsen S, Beiske K, Tjønnfjord GE | title = Primary chronic cold agglutinin disease: an update on pathogenesis, clinical features and therapy | journal = Hematology | volume = 12 | issue = 5 | pages = 361–370 | date = October 2007 | pmid = 17891600 | pmc = 2409172 | doi = 10.1080/10245330701445392 }}</ref> *** Rh disease,<ref name="Mitchell-2007" /> one of the causes of hemolytic disease of the newborn *** Transfusion reaction to blood transfusions<ref name="Mitchell-2007" /> ** Mechanical trauma to red blood cells *** Microangiopathic hemolytic anemias, including thrombotic thrombocytopenic purpura and disseminated intravascular coagulation<ref name="Mitchell-2007" /> *** Mechanical heart valves and blood pumps.<ref>{{Cite web |title=Hemolytic Anemia |url=https://www.hopkinsmedicine.org/health/conditions-and-diseases/hemolytic-anemia |access-date=19 April 2026 |website=Johns Hopkins Medicine}}</ref><ref>{{Cite journal |last=Köhne |first=Inge |date=September 2020 |title=Haemolysis induced by mechanical circulatory support devices: unsolved problems |journal=Perfusion |volume=35 |issue=6 |pages=474–483 |doi=10.1177/0267659120931307 |issn=1477-111X |pmc=7416332 |pmid=32571178}}</ref> ** Parasitic *** ''Trypanosoma congolense'' causes the disease nagana in cattle and other domesticated animals.<ref name="Stijlemans-2007">{{cite journal |last1=Stijlemans |first1=Benoît |last2=Guilliams |first2=Martin |last3=Raes |first3=Geert |last4=Beschin |first4=Alain |last5=Magez |first5=Stefan |last6=De Baetselier |first6=Patrick |title=African trypanosomosis: From immune escape and immunopathology to immune intervention |journal=Veterinary Parasitology |date=August 2007 |volume=148 |issue=1 |pages=3–13 |doi=10.1016/j.vetpar.2007.05.005 |pmid=17560035 }}</ref> *** Infection with the malaria parasite is a common cause of anemia across many tropical and subtropical regions.<ref name="Mitchell-2007" /> ** Breakdown of hemoglobin *** Heinz body anemia, which may be caused by G6PD deficiency, or through oxidative damage by administered drugs.<ref>{{Citation |last=Herman |first=Timothy F. |title=Heinz Body |date=2023-06-08 |work=StatPearls [Internet] |url=https://www.ncbi.nlm.nih.gov/sites/books/NBK551622/ |access-date=2026-04-07 |publisher=StatPearls Publishing |language=en |pmid=31869086 |last2=Killeen |first2=Robert B. |last3=Javaid |first3=Muhammad U.}}</ref>

===Blood loss=== * Trauma<ref name="Mitchell-2007" /> * Gastrointestinal blood loss: ** Lesions, leading to either acute bleeds (e.g. variceal lesions, peptic ulcers, hemorrhoids<ref>{{cite web | url=https://lacolon.com/article/hemorrhoids-iron-deficiency-can-hemorrhoids-cause-iron-deficiency-anemia | title=Do Hemorrhoids Cause Iron Deficiency Anemia? | date=26 June 2018 }}</ref>) or chronic blood loss (e.g. angiodysplasia).<ref name="Mitchell-2007" /> ** Chronic bleeding due to infection by intestinal nematodes feeding on blood, such as hookworms<ref>{{cite journal | vauthors = Brooker S, Hotez PJ, Bundy DA | title = Hookworm-related anaemia among pregnant women: a systematic review | journal = PLOS Neglected Tropical Diseases | volume = 2 | issue = 9 | article-number = e291 | date = September 2008 | pmid = 18820740 | pmc = 2553481 | doi = 10.1371/journal.pntd.0000291 | doi-access = free | bibcode = 2008PNTDi...2..291B }}</ref><ref name="Dugdale-2001" /> and the whipworm ''Trichuris trichiura'' <ref>{{cite journal | vauthors = Gyorkos TW, Gilbert NL, Larocque R, Casapía M | title = Trichuris and hookworm infections associated with anaemia during pregnancy | journal = Tropical Medicine & International Health | volume = 16 | issue = 4 | pages = 531–537 | date = April 2011 | pmid = 21281406 | doi = 10.1111/j.1365-3156.2011.02727.x | s2cid = 205391965 | doi-access = }}</ref> * Gynecologic disturbances:<ref name="Mitchell-2007" /> ** From abnormally heavy menstruation<ref>{{Cite web |last=Erdik |first=Baran |date=2023-05-07 |title=Anemia From Period: Symptoms, Treatment, And Complications |url=https://healthmatch.io/anemia/anemia-from-period |access-date=2026-04-12 |website=HealthMatch |language=en}}</ref> ** Repeated pregnancies and short birth intervals.<ref name="Dugdale-2001" /> * Many types of cancers, such as leukemia and multiple myeloma, may cause acute or chronic blood loss.<ref name="CancerSoc-2025">{{Cite web |date=26 February 2025 |title=Is Anemia a Sign of Cancer? |url=https://www.cancer.org/cancer/diagnosis-staging/signs-and-symptoms-of-cancer/anemia.html |access-date=2026-04-12 |website=The American Cancer Society |language=en}}</ref> * Anemia caused by medical interventions (Iatrogenic anemia): acute blood loss blood loss from repeated blood draws, surgical procedures, or as a side effect of chemotherapy.<ref name="Whitehead-2019">{{cite journal |last1=Whitehead |first1=Nedra S. |last2=Williams |first2=Laurina O. |last3=Meleth |first3=Sreelatha |last4=Kennedy |first4=Sara M. |last5=Ubaka-Blackmoore |first5=Nneka |last6=Geaghan |first6=Sharon M. |last7=Nichols |first7=James H. |last8=Carroll |first8=Patrick |last9=McEvoy |first9=Michael T. |last10=Gayken |first10=Julie |last11=Ernst |first11=Dennis J. |last12=Litwin |first12=Christine |last13=Epner |first13=Paul |last14=Taylor |first14=Jennifer |last15=Graber |first15=Mark L. |title=Interventions to prevent iatrogenic anemia: a Laboratory Medicine Best Practices systematic review |journal=Critical Care |date=December 2019 |volume=23 |issue=1 |page=278 |doi=10.1186/s13054-019-2511-9 |pmid=31399052 |pmc=6688222 |doi-access=free }}</ref><ref name="Martin-2015">{{cite journal |last1=Martin |first1=Niels D. |last2=Scantling |first2=Dane |title=Hospital-Acquired Anemia: A Contemporary Review of Etiologies and Prevention Strategies |journal=Journal of Infusion Nursing |date=September 2015 |volume=38 |issue=5 |pages=330–338 |doi=10.1097/NAN.0000000000000121 |pmid=26339939 |s2cid=30859103 }}</ref><ref name="CancerSoc-2025" />

===Fluid overload=== Fluid overload (hypervolemia) causes decreased hemoglobin concentration and apparent anemia:<ref>{{cite journal |last1=Hung |first1=Szu-Chun |last2=Kuo |first2=Ko-Lin |last3=Peng |first3=Ching-Hsiu |last4=Wu |first4=Che-Hsiung |last5=Wang |first5=Yi-Chun |last6=Tarng |first6=Der-Cherng |title=Association of Fluid Retention With Anemia and Clinical Outcomes Among Patients With Chronic Kidney Disease |journal=Journal of the American Heart Association |year=2015 |volume=4 |issue=1 |article-number=e001480 |doi=10.1161/JAHA.114.001480 |pmc=4330071 |pmid=25559015}}</ref> * General causes of hypervolemia include excessive sodium or fluid intake, sodium or water retention.<ref name="Hagerstwon">{{cite book | chapter = Fluid imbalances|title=Portable Fluids and Electrolytes (Portable Series) |publisher=Lippincott Williams & Wilkins|location=Hagerstwon, MD |year=2007 |page= 62 |isbn=978-1-58255-678-9 }}</ref> * During early pregnancy, hormonal changes trigger an increase in blood plasma volume, while red cell mass increases more slowly. This physiological change dilutes existing RBCs and may trigger a diagnosis of anemia.<ref name="Dugdale-2001" /><ref>{{cite web|url=http://www.isbtweb.org/working-parties/clinical-transfusion/8-obstetric-anaemia/|title=ISBT: 8. Obstetric anaemia|website=www.isbtweb.org|language=en|access-date=2018-05-22}}</ref>

=== General global contributors === * In many regions, nutritional deficiencies are major drivers of reduced RBC production. Poor intake of iron, folate, and vitamin B₁₂ can significantly impair hemoglobin synthesis and erythropoiesis. This is especially common in low-income populations, areas with limited food diversity, and communities experiencing famine.<ref name="Dugdale-2001" /> Socioeconomic factors such as poverty, limited access to nutrient-rich foods, and high rates of parasitic exposure increase the risk of iron-deficiency anemia in women and children.<ref name="Dugdale-2001" /> * Pregnancy greatly increases iron requirements, and inadequate dietary intake during pregnancy is one of the leading causes of anemia among reproductive-age women worldwide.<ref name="Dugdale-2001" /> * Chronic infections common in developing countries, such as malaria and hookworm disease, impair erythropoiesis either through inflammatory suppression or recurrent blood loss leading to iron depletion.<ref name="Dugdale-2001" />

== Classification systems == Anemia is often classified by the size of red blood cells, visible in a peripheral blood smear. The mean corpuscular volume (MCV) of a normal RBC is between 80 and 100 femtoliters. If the cells are smaller than 80 fl, the anemia is said to be microcytic; if they are larger than 100 fl, the anemia is macrocytic. Within the normal range, the anemia is normocytic.<ref name="Turner-2023">{{Citation |last=Turner|first=Jake|title=Anemia|date=8 August 2023|work=StatPearls|url=http://www.ncbi.nlm.nih.gov/books/NBK499994/|access-date=2026-04-01|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=29763170|last2=Parsi|first2=Meghana|last3=Badireddy|first3=Madhu}}</ref>

The most common causes of microcytic anemia are iron deficiency, thalassemia, and chronic diseases such as autoimmunity or cancer.<ref name="Turner-2023" /><ref>{{Cite web |title=What Is Microcytic Anemia?|url=https://my.clevelandclinic.org/health/diseases/23015-microcytic-anemia|archive-url=http://web.archive.org/web/20260303192530/https://my.clevelandclinic.org/health/diseases/23015-microcytic-anemia|archive-date=2026-03-03|access-date=2026-04-02|website=Cleveland Clinic|language=en|date=June 2024}}</ref> Macrocytic anemia can be caused by e.g. vitamin deficiency (B₁₂ or folate), alcohol use disorder, or hypothyroidism.<ref name="Turner-2023" /> Normocytic anemias include those caused by blood loss, some chronic diseases, or kidney disease.<ref name="Turner-2023" /><ref>{{Cite web |title=What Is Normocytic Anemia?|url=https://my.clevelandclinic.org/health/diseases/22977-normocytic-anemia|access-date=2026-04-02|website=Cleveland Clinic|language=en|date=October 2022}}</ref>

The other principal principle method of classification looks at the balance between erythropoiesis (RBC production in the bone marrow) and eryptosis (RBC breakdown, principally in the spleen). Anemias in which the bone marrow fails to make sufficient RBCs are termed hypoproliferative; included in this group are nutrient deficiencies (e.g. iron, B₁₂, folate), thalassemia, and cancers which affect the bone marrow.<ref name="Turner-2023" /> When production is normal but there is excessively rapid breakdown of RBCs, the term is hemolytic anemia. This group includes sickle cell anemia, malaria, glucose-6-phosphate dehydrogenase deficiency and some autoimmune conditions such as lupus.<ref>{{Cite web |title=Hemolytic Anemia {{!}} Symptoms, Diagnosis & Treatment|url=https://www.cincinnatichildrens.org/health/h/hemolytic-anemia|access-date=2026-04-06|website=www.cincinnatichildrens.org}}</ref><ref>{{Cite web |title=Glucose-6-phosphate dehydrogenase deficiency: MedlinePlus Genetics|url=https://medlineplus.gov/genetics/condition/glucose-6-phosphate-dehydrogenase-deficiency/|access-date=2026-04-06|website=National Library of Medicine|language=en}}</ref> Acute anemia caused by blood loss - e.g. following injury, surgery or childbirth - doesn't fit into this classification.<ref>{{Citation |last=Killeen|first=Robert B.|title=Acute Anemia|date=26 February 2025|work=StatPearls|url=http://www.ncbi.nlm.nih.gov/books/NBK537232/|access-date=2026-04-06|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=30725917|last2=Kaur|first2=Anahat|last3=Afzal|first3=Muriam}}</ref>

=== Transfusion dependence === Anemia is classified as transfusion-dependent if regular blood transfusions are required to maintain quality of life, or to prevent death.<ref>{{cite journal | vauthors = Gale RP, Barosi G, Barbui T, Cervantes F, Dohner K, Dupriez B, Gupta V, Harrison C, Hoffman R, Kiladjian JJ, Mesa R, Mc Mullin MF, Passamonti F, Ribrag V, Roboz G, Saglio G, Vannucchi A, Verstovsek S | display-authors = 6 | title = What are RBC-transfusion-dependence and -independence? | journal = Leukemia Research | volume = 35 | issue = 1 | pages = 8–11 | date = January 2011 | pmid = 20692036 | doi = 10.1016/j.leukres.2010.07.015 | pmc = 8215731 }}</ref> Most people with myelodysplastic syndrome develop this state at some point in time.<ref name="Melchert-2007" /> Beta thalassemia may also result in transfusion dependence.<ref>{{cite book |last1=Hillyer |first1=Christopher D. |last2=Silberstein |first2=Leslie E. |last3=Ness |first3=Paul M. |last4=Anderson |first4=Kenneth C. |last5=Roback |first5=John D. |title=Blood Banking and Transfusion Medicine: Basic Principles and Practice |date=2006 |publisher=Elsevier Health Sciences |isbn=978-0-7020-3625-5 |page=534 |url=https://books.google.com/books?id=8iEPDQAAQBAJ&pg=PT556 }}</ref><ref>{{cite book |last1=Mandel |first1=Jess |last2=Taichman |first2=Darren |title=Pulmonary Vascular Disease |date=2006 |publisher=Elsevier Health Sciences |isbn=978-1-4160-2246-6 |page=170 |url=https://books.google.com/books?id=v-pr4P34QjIC&pg=PA170 |language=en}}</ref> Concerns from repeated blood transfusions include iron overload,<ref name="Melchert-2007">{{cite journal | vauthors = Melchert M, List AF | title = Management of RBC-transfusion dependence | journal = Hematology. American Society of Hematology. Education Program | volume = 2007 | pages = 398–404 | date = 2007 | pmid = 18024657 | doi = 10.1182/asheducation-2007.1.398 | doi-access = free }}</ref> which may require chelation therapy.<ref>{{cite book |last1=Ferri |first1=Fred F. |title=BOPOD – Ferri's Clinical Advisor 2016 |date=2015 |publisher=Elsevier Health Sciences |isbn=978-0-323-37822-2 |page=1131.e2 |url=https://books.google.com/books?id=bbLSCQAAQBAJ&pg=PA1131-IA2 |language=en}}</ref>

==Treatment==

=== Cause === Treatment of anemia depends entirely on establishing the underlying cause.<ref name="Mayo-2022b">{{cite web |date=11 May 2023|title=Anemia – Symptoms and causes|url=https://www.mayoclinic.org/diseases-conditions/anemia/symptoms-causes/syc-20351360|access-date=2022-04-01|website=Mayo Clinic|language=en}}</ref>

==== Acute anemia ==== Acute anemia is typically caused by sudden loss of blood, e.g. through injury, hemorrhage, or breakdown of red blood cells as in malaria or some conditions causing acute hemolysis. This can be relieved with supplemental oxygen or blood transfusion. Provided the root cause can be fixed, these treatments can be discontinued as recovery takes place and the body naturally replaces the lost blood cells.<ref>{{Citation |last=Killeen|first=Robert B.|title=Acute Anemia|date=2026|work=StatPearls|url=http://www.ncbi.nlm.nih.gov/books/NBK537232/|access-date=2026-04-21|place=Treasure Island (FL)|publisher=StatPearls Publishing|pmid=30725917|last2=Kaur|first2=Anahat|last3=Afzal|first3=Muriam}}</ref>

==== Deficiency anemias ==== The most common cause of anemia is iron deficiency, and the most common cause of this is poor diet, especially in low income communities. Other common deficiencies causing anemia are vitamin B<small>₁₂</small> and folate. Treatment for these involves supplements - iron or B<small>₁₂</small> (either as tablet or injection) or folate (as tablet).<ref name="BUPA-2026">{{Cite web |title=Anaemia: Symptoms, causes and treatment {{!}} Bupa UK|url=https://www.bupa.co.uk/health-information/heart-blood-circulation/anaemia|access-date=2026-04-20|website=www.bupa.co.uk|language=en-GB}}</ref> Changes to diet will be recommended if poor diet is causing or contributing to the anemia.<ref name="BUPA-2026" /> Other contributing factors - e.g. intestinal disease affecting the absorption of nutrients, or hookworm infection - must also be treated.<ref name="NHS-2024">{{Cite web |date=26 January 2024|title=Iron deficiency anaemia|url=https://www.nhs.uk/conditions/iron-deficiency-anaemia/|access-date=2026-04-21|website=National Health Service|language=en}}</ref><ref>{{Cite web |title=Understanding Hookworm {{!}} UMass Memorial Health|url=https://www.ummhealth.org/health-library/understanding-hookworm|access-date=2026-04-24|website=www.ummhealth.org|language=en}}</ref> For women with severe menstrual bleeding which leads to iron deficiency, hormone treatment may be effective.<ref name="NHS-2024" />

==== Hereditary anemias ==== The most common hereditary causes of anemia are sickle-cell disease (causing increased hemolysis) and thalassemia (reduced production of hemoglobin).<ref name="Cleveland Clinic-2024">{{Cite web |date=16 April 2024|title=Anemia|url=https://my.clevelandclinic.org/health/diseases/3929-anemia|website=Cleveland Clinic}}</ref> Less common are hereditary spherocytosis and G6PD Deficiency.<ref name="Dx&TxGuidelines">{{Cite journal |last1=Bolton-Maggs|first1=P. H. B.|last2=Stevens|first2=R. F.|last3=Dodd|first3=N. J.|last4=Lamont|first4=G.|last5=Tittensor|first5=P.|last6=King|first6=M. -J.|author7=General Haematology Task Force of the British Committee for Standards in Haematology|year=2004|title=Guidelines for the diagnosis and management of hereditary spherocytosis|journal=British Journal of Haematology|volume=126|issue=4|pages=455–474|doi=10.1111/j.1365-2141.2004.05052.x|pmid=15287938|s2cid=5870305|doi-access=}}</ref><ref name="Frank-2005b">{{Cite journal |last=Frank|first=Jennifer E.|date=2005-10-01|title=Diagnosis and Management of G6PD Deficiency|url=https://www.aafp.org/afp/2005/1001/p1277.html|journal=American Family Physician|volume=72|issue=7|pages=1277–1282|issn=0002-838X|pmid=16225031}}</ref> Generally speaking, mild cases can cause few symptoms and either need no treatment or can be managed by means of avoiding circumstances which might trigger a crisis, monitoring and occasional treatment. More severe cases may need be treated by blood transfusion or surgical removal of the spleen.<ref name="Cleveland Clinic-2024" /> Sickle-cell disease and thalassemia may also be treated by means of stem cell transplantation.<ref>{{Cite journal |last=Lucarelli|first=Guido|last2=Isgrò|first2=Antonella|last3=Sodani|first3=Pietro|last4=Gaziev|first4=Javid|date=2012-05-01|title=Hematopoietic Stem Cell Transplantation in Thalassemia and Sickle Cell Anemia|url=http://perspectivesinmedicine.cshlp.org/content/2/5/a011825|journal=Cold Spring Harbor Perspectives in Medicine|language=en|volume=2|issue=5|article-number=a011825|doi=10.1101/cshperspect.a011825|issn=2157-1422|pmc=3331690|pmid=22553502}}</ref>

==== Iatrogenic anemias ==== Iatrogenic anemias are caused by medical interventions.<ref name="Martin-2015a">{{cite journal|last1=Martin|first1=Niels D.|last2=Scantling|first2=Dane|title=Hospital-Acquired Anemia|journal=Journal of Infusion Nursing|volume=38|issue=5|year=2015|pages=330–338|issn=1533-1458|doi=10.1097/NAN.0000000000000121|pmid=26339939|s2cid=30859103}}</ref> Most common is repeated blood draws, e.g. while in hospital critical care. This can be mitigated by minimising the frequency or volume of blood taken, and by blood transfusion.<ref name="Eaton-2017">{{cite journal|last1=Eaton|first1=Kevin P.|last2=Levy|first2=Kathryn|last3=Soong|first3=Christine|last4=Pahwa|first4=Amit K.|last5=Petrilli|first5=Christopher|last6=Ziemba|first6=Justin B.|last7=Cho|first7=Hyung J.|last8=Alban|first8=Rodrigo|last9=Blanck|first9=Jaime F.|last10=Parsons|first10=Andrew S.|title=Evidence-Based Guidelines to Eliminate Repetitive Laboratory Testing|journal=JAMA Internal Medicine|volume=177|issue=12|year=2017|pages=1833–1839|issn=2168-6106|doi=10.1001/jamainternmed.2017.5152|pmid=29049500|s2cid=40475834}}</ref> Some forms of chemotherapy can cause anemia; if the regimen cannot be changed, transfusions are necessary.<ref name="Rodgers-2008">{{cite journal |vauthors=Rodgers GM, Becker PS, Bennett CL, Cella D, Chanan-Khan A, Chesney C, Cleeland C, Coccia PF, Djulbegovic B, Garst JL, Gilreath JA, Kraut EH, Lin WC, Matulonis U, Millenson M, Reinke D, Rosenthal J, Sabbatini P, Schwartz RN, Stein RS, Vij R|date=July 2008|title=Cancer- and chemotherapy-induced anemia|journal=Journal of the National Comprehensive Cancer Network|volume=6|issue=6|pages=536–64|doi=10.6004/jnccn.2008.0042|pmid=18597709}}</ref>

=== Principal methods of treatment ===

==== Iron supplementation ==== Iron deficiency results in the decreased production of hemoglobin, the oxygen-carrying protein in red blood cells.<ref name="Nguyen-Statpearls-2026">{{Citation |last=Nguyen |first=Minhthao |title=Iron Supplementation |date=2026 |work=StatPearls |url=http://www.ncbi.nlm.nih.gov/books/NBK557376/ |access-date=2026-04-23 |place=Treasure Island (FL) |publisher=StatPearls Publishing |pmid=32491308 |last2=Tadi |first2=Prasanna}}</ref> Mild to moderate iron-deficiency anemia is treated by iron supplementation in the diet.<ref name="Nguyen-Statpearls-2026" /> In cases where this is either ineffective, would be too slow (for example, pre-operatively), or where absorption is impeded (for example, in cases of inflammation), iron supplementation can be given intravenously.<ref name="Nguyen-Statpearls-2026" />

==== Blood transfusions ==== alt=Image of blood bag labeled with blood type AB+|thumb|Blood bag used for blood transfusion Blood transfusion is the process of transferring blood products into a person's circulation intravenously.<ref>{{cite web|url=https://www.nhlbi.nih.gov/health/blood-bone-marrow-treatments|title=Blood Transfusion|publisher=National Heart, Lung, and Blood Institute (NHLBI)|access-date=2019-06-16|archive-date=2019-06-23|archive-url=https://web.archive.org/web/20190623181239/https://www.nhlbi.nih.gov/health-topics/blood-transfusion|url-status=live}}</ref> Transfusion is generally recommended if hemoglobin falls below 70 to 80 grams/liter.<ref>{{cite journal |vauthors=Carson JL, Stanworth SJ, Dennis JA, Trivella M, Roubinian N, Fergusson DA, Triulzi D, Dorée C, Hébert PC|display-authors=6|title=Transfusion thresholds for guiding red blood cell transfusion|journal=The Cochrane Database of Systematic Reviews|volume=12|issue=12|article-number=CD002042|date=December 2021|pmid=34932836|pmc=8691808|doi=10.1002/14651858.CD002042.pub5}}</ref>{{Update inline|reason=Updated version https://www.ncbi.nlm.nih.gov/pubmed/41114449|date = May 2026}} Prior to transfusion, the donated blood is carefully crossmatch<nowiki/>ed with the patient's blood to ensure compatibility. During transfusion, the patient is monitored for any side effects.<ref name="NHLBI-Treatments-2022">{{Cite web |date=2022-03-24 |title=Treatments for Blood Disorders - Treatments for Blood Disorders {{!}} NHLBI, NIH |url=https://www.nhlbi.nih.gov/health/blood-bone-marrow-treatments |access-date=2026-04-28 |website=www.nhlbi.nih.gov |language=en}}</ref>

==== Bone marrow transplant ==== alt=Illustration labeled "Allogenic transplant" showing the femur with a large needle puncturing into the medullary cavity to harvest red bone marrow containing blood stem cells|thumb|Procedure of harvesting blood stem cells for transplantation

Red blood cells are manufactured in the bone marrow. A bone marrow transplant may be recommended if the marrow is unable to produce enough red blood cells, as for example in aplastic anemia.<ref name="Johns Hopkins Medicine">Johns Hopkins Medicine. (n.d.). ''Aplastic anemia''. The Johns Hopkins University & Health System. Retrieved October 19, 2025 <nowiki>https://www.hopkinsmedicine.org/kimmel-cancer-center/cancers-we-treat/blood-bone-marrow-cancers/aplastic-anemia</nowiki></ref> In a bone marrow transplant, old defective bone marrow is destroyed using drugs and replaced with new stem cells from a compatible donor.<ref name="NHLBI-Treatments-2022" />

==== Vitamin B₁₂ ==== In severe cases where vitamin B₁₂ diet is not being absorbed in the intestine, it can instead be supplemented via intramuscular injection. Pernicious anemia, for example, is a type of vitamin B₁₂ deficiency anemia that results from lack of intrinsic factor.<ref name="NHLBI-2011">{{Cite web |date=April 1, 2011|title=What Is Pernicious Anemia?|url=https://www.nhlbi.nih.gov/health/health-topics/topics/prnanmia|archive-url=https://web.archive.org/web/20160314111724/https://www.nhlbi.nih.gov/health/health-topics/topics/prnanmia|archive-date=14 March 2016|access-date=14 March 2016|website=National Heart, Lung, and Blood Institute.}}</ref> Vitamin B₁₂ injections, initially given daily, are quick-acting, and symptoms usually go away within one to two weeks.<ref name="Langan-2017">{{cite journal |last1=Langan |first1=Robert C. |last2=Goodbred |first2=Andrew J. |date=2017-09-15 |title=Vitamin B12 Deficiency: Recognition and Management |url=https://www.aafp.org/pubs/afp/issues/2017/0915/p384.html |journal=American Family Physician |language=en-US |volume=96 |issue=6 |pages=384–389|pmid=28925645 }}</ref> As the condition improves, doses are reduced in frequency. In some cases lifelong treatment may be needed.<ref>{{cite web |date=2017-09-14 |title=Pernicious Anemia Clinical Presentation: History, Physical Examination |url=http://emedicine.medscape.com/article/204930-clinical#b3 |access-date=2022-08-04 |website= |archive-url=https://web.archive.org/web/20170914062810/http://emedicine.medscape.com/article/204930-clinical#b3 |archive-date=14 September 2017 }}</ref>

==== Erythropoiesis-stimulating agents ==== Erythropoiesis-stimulating agents (ESA) work to increase production of erythropoietin, a hormone that increases the production of red blood cells.<ref name="Schoener-Statpearls-2025">Schoener, Benjamin; Borger, Judith (2025), "Erythropoietin Stimulating Agents", ''StatPearls'', Treasure Island (FL): StatPearls Publishing, PMID 30725682, retrieved 2025-10-19</ref> They are used to treat anemia due to end stage kidney disease, chemotherapy, major surgery, or certain treatments in HIV/AIDS.<ref name="FDA2017">{{Cite web |date=31 March 2017|title=Information on Erythropoiesis-Stimulating Agents (ESA) Epoetin alfa (marketed as Procrit, Epogen), Darbepoetin alfa (marketed as Aranesp)|url=https://www.fda.gov/Drugs/DrugSafety/ucm109375.htm|archive-url=https://web.archive.org/web/20220414123615/https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/information-erythropoiesis-stimulating-agents-esa-epoetin-alfa-marketed-procrit-epogen-darbepoetin|archive-date=14 April 2022|website=US Food and Drug Administration – Drug Safety Information}}</ref><ref name="Banzi-2016">{{Cite report |url=https://www.who.int/selection_medicines/committees/expert/21/applications/s10_erythropoietins_add.pdf|title=WHO EML 2016-2017 - Application for erythropoietin-stimulating agents (erythropoietin type blood factors)|last1=Banzi|first1=Rita|last2=Gerardi|first2=Chiara|date=23 December 2016|publisher=WHO|id=WHO EML 2016–2017, Version 3|archive-url=https://web.archive.org/web/20200831023346/https://www.who.int/selection_medicines/committees/expert/21/applications/s10_erythropoietins_add.pdf|archive-date=31 August 2020}}</ref> In these situations they decrease the need for blood transfusions.<ref name="Banzi-2016" />

==Epidemiology== Anemia affects 24% of the world's population, with iron-deficiency anemia accounting for the majority of cases.<ref name="Gardner-2023">{{Cite journal |last1=Gardner |first1=William M |last2=Razo |first2=Christian |last3=McHugh |first3=Theresa A |last4=Hagins |first4=Hailey |last5=Vilchis-Tella |first5=Victor M |last6=Hennessy |first6=Conor |last7=Taylor |first7=Heather Jean |last8=Perumal |first8=Nandita |last9=Fuller |first9=Kia |last10=Cercy |first10=Kelly M |last11=Zoeckler |first11=Leo Zucker |last12=Chen |first12=Catherine S |last13=Lim |first13=Stephen S |last14=Aali |first14=Amirali |last15=Abate |first15=Kalkidan Hassen |date=2023 |title=Prevalence, years lived with disability, and trends in anaemia burden by severity and cause, 1990–2021: findings from the Global Burden of Disease Study 2021 |journal=The Lancet Haematology |language=English |volume=10 |issue=9 |pages=e713–e734 |doi=10.1016/S2352-3026(23)00160-6 |pmid=37536353 |pmc=10465717 |issn=2352-3026 }}</ref>

=== Geographical trends === Globally, anemia is most common in the tropical areas of sub-Saharan Africa and South Asia. {{As of|2021}}, anemia affected 47.4% of the population in Western sub-Saharan Africa and 35.7% in South Asia.<ref name=":0">{{Cite web |date=31 July 2023|title=The Lancet: New study reveals global anemia cases remain persistently high among women and children. Anemia rates decline for men. {{!}} Institute for Health Metrics and Evaluation|url=https://www.healthdata.org/news-events/newsroom/news-releases/lancet-new-study-reveals-global-anemia-cases-remain-persistently|access-date=2026-05-18|website=www.healthdata.org|language=en}}</ref> This is due to a combination of combination of poor diet (contributing to iron deficiency), parasitic diseases, and hemoglobinopathies such as sickle cell disease. Women of reproductive age are more at risk due to blood loss during menstruation or childbirth.<ref name=":0" />

=== Population groups at higher risk === Generally speaking, the very young and the very old have a higher risk of anemia than the general population. In the first few months after birth, babies have a natural dip in hemoglobin levels (physiologic anemia) as their body adjusts to life outside the womb;<ref>{{Cite web |last=Walter|first=Andrew W.|date=November 2024|title=Perinatal Anemia - Pediatrics|url=https://www.msdmanuals.com/professional/pediatrics/perinatal-hematologic-disorders/perinatal-anemia|access-date=2026-05-19|website=MSD Manual Professional Edition|language=en}}</ref> this can be aggravated by other factors such as premature birth, blood loss, and consumption of cow's milk.<ref>{{Cite journal |last=Ziegler|first=Ekhard E|date=November 2011|title=Consumption of cow's milk as a cause of iron deficiency in infants and toddlers: Nutrition Reviews©, Vol. 69, No. S1|url=https://academic.oup.com/nutritionreviews/article-lookup/doi/10.1111/j.1753-4887.2011.00431.x|journal=Nutrition Reviews|language=en|volume=69|pages=S37–S42|doi=10.1111/j.1753-4887.2011.00431.x|url-access=subscription}}</ref> As children grow, they have a proportionately higher need for iron in their diet compared with adults, and are at risk of anemia if they have a poor diet.<ref>{{Cite web |last=|first=|date=February 2024|title=Iron deficiency in children: Prevention tips for parents|url=https://www.mayoclinic.org/healthy-lifestyle/childrens-health/in-depth/iron-deficiency/art-20045634|access-date=2026-05-19|website=Mayo Clinic|language=en}}</ref>

Women of reproductive age have enhanced risk of anemia.<ref>{{Cite journal |last=Obeagu|first=Getrude Uzoma|last2=Obeagu|first2=Emmanuel Ifeanyi|date=2025-08-29|title=Complications of anemia in pregnancy: An updated overview for healthcare professionals|url=https://journals.lww.com/10.1097/MD.0000000000044246|journal=Medicine|language=en|volume=104|issue=35|pages=|doi=10.1097/MD.0000000000044246|issn=1536-5964|pmc=12401385|pmid=40898523}}</ref> This could be associated with loss of blood during menstruation, or with pregnancy. In normal pregnancies, a natural increase in plasma volume is not matched by an increase in RBC mass leading to a mild decrease in hemoglobin concentration referred to as physiologic (or dilutional) anemia.<ref>{{Cite journal |author1=American College of Obstetricians Gynecologists' Committee on Practice Bulletins—Obstetrics|date=August 2021|title=Anemia in Pregnancy: ACOG Practice Bulletin, Number 233|url=https://journals.lww.com/10.1097/AOG.0000000000004477|journal=Obstetrics & Gynecology|language=en|volume=138|issue=2|pages=e55–e64|doi=10.1097/AOG.0000000000004477|issn=0029-7844|pmid=34293770|s2cid=236198933|url-access=subscription}}</ref> There is also a risk of blood loss during childbirth.<ref>{{Cite web |date=May 2024|title=Iron Deficiency Anaemia in pregnancy and after birth|url=https://digitalpatientinformationhub.bradfordhospitals.nhs.uk/leaflets/iron-deficiency-anaemia-in-pregnancy-and-after-birth/|access-date=2026-05-19|website=Digital patient information hub of Bradford Teaching Hospitals}}</ref>

The major inherited anemias, thalassemia and sickle cell, are prevalent in areas which are historically prone to malaria - Africa, the Mediterranean, the Middle East, and South Asia. They are now more widely distributed geographically among populations who originated in the areas; this is a consequence of the slave trade in the 18th and 19th centuries, and other causes of migration more recently.<ref>{{cite journal |vauthors=Kattamis A, Forni GL, Aydinok Y, Viprakasit V|date=December 2020|title=Changing patterns in the epidemiology of β-thalassemia|journal=European Journal of Haematology|volume=105|issue=6|pages=692–703|doi=10.1111/ejh.13512|pmc=7692954|pmid=32886826}}</ref><ref>{{cite journal |vauthors=Williams TN, Weatherall DJ|date=September 2012|title=World distribution, population genetics, and health burden of the hemoglobinopathies|journal=Cold Spring Harbor Perspectives in Medicine|volume=2|issue=9|article-number=a011692|doi=10.1101/cshperspect.a011692|pmc=3426822|pmid=22951448}}</ref>

=== Socioeconomic status === Deficiency anemias (iron, B₁₂ or folate deficiency) are strongly linked with low socioeconomic status. This is attributed to a combination of poor diet and poor health literacy. This translates geographically into a high incidence of these anemias in low and middle-income countries. Low income groups in developed countries also show an increased incidence of anemia.<ref>{{Cite web |title=Anaemia|url=https://www.who.int/news-room/fact-sheets/detail/anaemia|access-date=2026-05-21|website=www.who.int|language=en}}</ref><ref>{{Cite journal |last=Ritchie|first=Hannah|date=2024-11-25|title=Billions of people suffer from anemia, but there are cheap ways to reduce this|url=https://ourworldindata.org/billions-people-suffer-anemia-cheap-ways-reduce|journal=Our World in Data|language=en}}</ref><ref>{{Cite journal |last=Smith|first=Margaret|last2=Drakesmith|first2=Cynthia Wright|last3=Haynes|first3=Sarah|last4=Maynard|first4=Suzanne|last5=Shah|first5=Akshay|last6=Roy|first6=Noemi BA|last7=Lee|first7=Joseph Jonathan|last8=Maurer|first8=Katja|last9=Stanworth|first9=Simon J.|last10=Bankhead|first10=Clare R.|date=2025-04-01|title=Prevalence and patterns of testing for anaemia in primary care in England: a cohort study using an electronic health records database|url=https://bjgp.org/content/75/753/e232|journal=British Journal of General Practice|language=en|volume=75|issue=753|pages=e232–e240|doi=10.3399/BJGP.2024.0336|issn=0960-1643|pmc=11881008|pmid=39658076}}</ref><ref>{{Citation |last=Williams|first=Anne M.|title=Anemia Prevalence: United States, August 2021–August 2023|date=December 2024|work=NCHS Data Briefs [Internet]|url=https://www.ncbi.nlm.nih.gov/books/NBK612586/|access-date=2026-05-21|publisher=National Center for Health Statistics (US)|language=en|pmid=40048464|last2=Ansai|first2=Nicholas|last3=Ahluwalia|first3=Namanjeet|last4=Nguyen|first4=Duong T.}}</ref>

==History== Signs of severe anemia in human bones from 4000 years ago have been uncovered in Thailand.<ref>{{cite journal |vauthors=Tayles N|title=Anemia, genetic diseases, and malaria in prehistoric mainland Southeast Asia|journal=American Journal of Physical Anthropology|volume=101|issue=1|pages=11–27|date=September 1996|pmid=8876811|doi=10.1002/(SICI)1096-8644(199609)101:1<11::AID-AJPA2>3.0.CO;2-G}}</ref>

The first discovery and discussion of blood was in 1674 when Antoni van Leeuwenhoek described red blood cells (RBCs) as "small round globules." RBCs counterpart, hemoglobin, wasn't discovered until much later by FL Hünefeld in 1840. In 1746, Vincenzo Menghini showed that iron was concentrated in the red blood cells using a magnetic knife.<ref name="Sheftel-2012">{{Cite journal|title=The long history of iron in the Universe and in health and disease|journal=Biochimica et Biophysica Acta (BBA) - General Subjects|date=March 2012|issn=0006-3002|pmc=3258305|pmid=21856378|pages=161–187|volume=1820|issue=3|doi=10.1016/j.bbagen.2011.08.002|first1=Alex D.|last1=Sheftel|first2=Anne B.|last2=Mason|first3=Prem|last3=Ponka |bibcode=2012BBAcG1820..161S }}</ref> Between 1877-1885, many key tools emerged like hemocytometer (RBC count), hemoglobin measurement, and hematocrit measurement that allowed for quantitative diagnosis of blood.<ref name="Aird-2022">{{Cite web|title=Did you know that anemia was first named as a clinical entity in 1807? • The Blood Project|url=https://www.thebloodproject.com/did-you-know-that-anemia-was-recognized-as-a-clinical-construct-well-before-lab-tests-were-available/|website=The Blood Project|date=2022-05-12|access-date=2025-11-30|first=William|last=Aird}}</ref> By the 1920s it was confirmed by multiple different studies that iron existed in plasma. McCance and Widdowson showed that iron is not excreted from the body in 1938, and it was later confirmed that iron absorption is the main way the body regulates iron levels.{{Citation needed|date=May 2026}}

In ancient cultures, like Assyria and Mediterranean societies, used iron for medical treatments, however, this occurred before iron's biological role was understood. In the 1500s, Nicholas Monarde used iron's "healing powers" to treat gout, acne and hair loss.<ref name="Sheftel-2012" /> Anemia started out as a clinical entity in 1807. Early diagnosis of anemia in the early 1800s were based solely on physical examinations such as fatigue, paleness, sweating, difficulty breathing, and dizziness. It wasn't until late in the 1800s when new technologies allowed for a more in depth, lab-based diagnosis on anemia.<ref>{{Cite journal|title=Iron deficiency anemia, population health and frailty in a modern Portuguese skeletal sample|journal=PLOS ONE|date=2019-03-07|issn=1932-6203|pmc=6405098|pmid=30845224|article-number=e0213369|volume=14|issue=3|doi=10.1371/journal.pone.0213369|language=en|first1=Samantha M.|last1=Hens|first2=Kanya|last2=Godde|first3=Kristin M.|last3=Macak | bibcode=2019PLoSO..1413369H | doi-access=free }}</ref> In 1939, anemia was officially defined as "a deficiency of blood not due to hemorrhage".<ref name="Aird-2022" />

== References == {{Reflist}}

== External links == {{sister project links||d=Q5445|c=Category:Anemia|n=no|q=no|b=no|v=no|voy=no|m=no|mw=no|s=no|wikt=anemia|species=no}} * [https://www.who.int/news-room/fact-sheets/detail/anaemia WHO fact sheet on anaemia] * [https://medlineplus.gov/anemia.html Anemia, U.S. National Library of Medicine]

{{Medical condition classification and resources | DiseasesDB = 663 | ICD11 = {{ICD11|Anaemias or other erythrocyte disorders|224336967}} | ICD10 = {{ICD10|D|50||d|50}}-{{ICD10|D|64||d|60}} | ICD9 = {{ICD9|280}}-{{ICD9|285}} | MedlinePlus = 000560 | eMedicineSubj = med | eMedicineTopic = 132 | eMedicine_mult = {{eMedicine2|emerg|808}} {{eMedicine2|emerg|734}} | MeshID = D000740 }}

{{Diseases of RBCs}} {{Medicine}} {{Authority control}}

Category:Anemias Category:Hematopathology Category:Wikipedia medicine articles ready to translate Category:Wikipedia emergency medicine articles ready to translate Category:Transfusion medicine