{{for|the kelp genus|Macrocystis}} {{More citations needed|date=May 2021}} {{Infobox medical condition (new) | name = Macrocytosis thumb|center| | image = | alt = | caption = | pronounce = | field = Hematology | synonyms = Macrocytes | symptoms = Shortness of breath, weakness, heart murmur, tachycardia | complications = | onset = | duration = | types = | causes = Vitamin B12 deficiency, Folic acid deficiency, Malabsorption, Alcoholism | risks = Bone marrow failure, hematologic malignancy | diagnosis = Symptoms, Complete blood count, Peripheral blood smear, Vitamin B12 level, Red cell folate level | differential = | prevention = | treatment = | medication = | prognosis = | frequency = | deaths = }} '''Macrocytosis''' is a condition where red blood cells are larger than normal.<ref>{{Cite journal |last1=Kaferle |first1=Joyce |last2=Strzoda |first2=Cheryl E. |date=2009-02-01 |title=Evaluation of macrocytosis |journal=American Family Physician |volume=79 |issue=3 |pages=203–208 |issn=0002-838X |pmid=19202968}}</ref> These enlarged cells, also known as macrocytes, are defined by a mean corpuscular volume (MCV) that exceeds the upper reference range established by the laboratory and hematology analyzer (usually >110 fL).<ref>{{Cite book |last1=Woodruff |first1=James N. |url=https://books.google.com/books?id=XUtgDAAAQBAJ&pg=PA248 |title=Primary Care of Adult Women, An Issue of Obstetrics and Gynecology Clinics of North America |last2=Blanchard |first2=Anita K. |date=2016-06-11 |publisher=Elsevier Health Sciences |isbn=978-0-323-44623-5 |language=en}}</ref> Upon examination of a peripheral blood smear under microscope, these macrocytes appear larger than standard erythrocytes. Macrocytosis is a common morphological feature in neonatal peripheral blood.<ref>{{Cite book |last=Bain |first=Barbara J. |url=https://books.google.com/books?id=dckoCQAAQBAJ&dq=macrocytes+in+neonates&pg=PA74 |title=Blood Cells: A Practical Guide |date=2015-01-20 |publisher=John Wiley & Sons |isbn=978-1-118-81733-9 |language=en}}</ref> The presence of macrocytosis can indicate a range of conditions, from benign, treatable illnesses to more serious underlying disorders.

== Types == Macrocytes may be oval or round. Oval macrocytes (also called megalocytes)<ref>{{Cite book |last1=Anderson |first1=Shauna Christine |url=https://books.google.com/books?id=pB_fyiPkksUC&dq=oval+macrocyte+megalocyte&pg=PA12 |title=Atlas of Hematology |last2=Poulsen |first2=Keila |date=2003 |publisher=Lippincott Williams & Wilkins |isbn=978-0-7817-2662-7 |language=en}}</ref> are seen in conditions associated with dyserythropoiesis including megaloblastic anemia, myelodysplastic syndromes, Fanconi anemia and CDA type I & III. Round macrocytes are associated with other causes of macrocytosis.

== Causes == In humans, the most prevalent causes of macrocytosis are often linked to alcoholism and deficiencies in vitamin B{{sub|12}} or folate (vitamin B{{sub|9}}), or a combination of these factors.<ref>{{Cite book |last1=Pacholok |first1=Sally |url=https://books.google.com/books?id=I13L1WDTNeoC&q=vitamin+b12+and+folate+deficiency+are+common+causes+of+macrocytosis |title=Could It Be B12?: An Epidemic of Misdiagnoses |last2=Stuart |first2=Jeffrey J. |date=2011-01-01 |publisher=Linden Publishing |isbn=978-1-61035-065-5 |language=en}}</ref> These conditions can affect the production and development of red blood cells, leading to their enlargement. Another cause of macrocytosis is benign familial macrocytosis, which is a hereditary condition that does not present symptoms.<ref>{{Cite journal |date=2022-10-07 |title=Macrocytosis: Practice Essentials, Pathophysiology, Etiology |url=https://emedicine.medscape.com/article/203858-overview}}</ref> Despite the larger size of the red blood cells, individuals with this condition typically have normal red blood cell function. Causes of macrocytosis may include:

* Megaloblastic anemia due to deficiency or abnormal metabolism of vitamin B{{sub|12}} or folate ** Poor dietary intake, including due to strict veganism ** Increased requirements ** Pernicious anemia ** Malabsorption syndromes * Alcoholism * Smoking * Reticulocytosis due to hemolysis, blood loss and hematinics * Hypothyroidism * Myelodysplastic syndromes (MDS) * Congenital dyserythropoietic anemia * Aplastic anemia and bone marrow failure syndromes * Inherited disorders of DNA synthesis ** Homocystinuria ** Lesch–Nyhan syndrome ** Deficient enzymes for folate metabolism * Liver disease * Chronic obstructive pulmonary disorder (COPD) * Certain drugs, including folate antagonists, purine antagonists, tyrosine kinase inhibitors, anti-HIV drugs etc.

== Complications == Macrocytosis does not itself lead to complications. Prognosis depends on its cause.

==See also== * Macrocytic anemia * Myelodysplastic syndrome

==References== {{Reflist}}

== External links == {{Medical resources | DiseasesDB = 7688 | ICD10 = {{ICD10|D|75|8|d|70}} | ICD9 = {{ICD9|289.89}} | ICDO = | OMIM = | MedlinePlus = | eMedicineSubj = med | eMedicineTopic = 1381 }} {{Abnormal clinical and laboratory findings}} {{Alcohol and health}} {{Portal bar|Biology|Medicine}}

Category:Hematopathology Category:Abnormal clinical and laboratory findings for RBCs