{{Infobox medical condition (new) | name = Eosinopenia | image = Eosinophil 2.jpg | caption = An eosinophil in peripheral blood | | pronounce = | field = | synonyms = | symptoms = | complications = | onset = | duration = | types = | causes = | risks = | diagnosis = | differential = | prevention = | treatment = | medication = | prognosis = | frequency = | deaths = }} '''Eosinopenia''' is a condition where the number of eosinophils, a type of white blood cell, in circulating blood is lower than normal.<ref name=":02">{{Citation |last=Carter |first=C. M. |title=12.11 - Alterations in Blood Components |date=2018-01-01 |work=Comprehensive Toxicology (Third Edition) |pages=249–293 |editor-last=McQueen |editor-first=Charlene A. |place=Oxford |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-801238-3.64251-4 |isbn=978-0-08-100601-6 |pmc=7152208 }}</ref> Eosinophils are a type of granulocyte and consequently from the same cellular lineage as neutrophils, basophils, and mast cells.<ref name=":02" /><ref name=":1">{{Cite journal |last1=Gil |first1=H. |last2=Bouldoires |first2=B. |last3=Bailly |first3=B. |last4=Meaux Ruault |first4=N. |last5=Humbert |first5=S. |last6=Magy-Bertrand |first6=N. |date=March 2019 |title=L'éosinopénie en 2018 |url=https://linkinghub.elsevier.com/retrieve/pii/S0248866318311810 |journal=La Revue de Médecine Interne |language=fr |volume=40 |issue=3 |pages=173–177 |doi=10.1016/j.revmed.2018.11.008|pmid=30501929 |s2cid=54568107 |url-access=subscription }}</ref> Along with the other granulocytes, eosinophils are part of the innate immune system and contribute to the defense of the body from pathogens. The most widely understood function of eosinophils is in association with allergy and parasitic disease processes, though their functions in other pathologies are the subject of ongoing research.<ref name=":6">{{Cite journal |last1=Rosenberg |first1=Helene F. |last2=Foster |first2=Paul S. |date=June 2021 |title=Eosinophils and COVID-19: diagnosis, prognosis, and vaccination strategies |journal=Seminars in Immunopathology |language=en |volume=43 |issue=3 |pages=383–392 |doi=10.1007/s00281-021-00850-3 |issn=1863-2297 |pmc=7962927 |pmid=33728484}}</ref> The opposite phenomenon, in which the number of eosinophils present in the blood is higher than normal, is known as eosinophilia.
== Definition and diagnosis == The definition of eosinopenia varies in clinical practice, and normal eosinophil levels vary among the population.<ref name=":3">{{Cite journal |last1=Tashkin |first1=Donald P. |last2=Wechsler |first2=Michael E. |date=2018-01-17 |title=Role of eosinophils in airway inflammation of chronic obstructive pulmonary disease |journal=International Journal of Chronic Obstructive Pulmonary Disease |language=English |volume=13 |pages=335–349 |doi=10.2147/COPD.S152291 |pmc=5777380 |pmid=29403271 |doi-access=free }}</ref> One common definition is an absolute eosinophil count of less than 50 cells/μLiter of blood.<ref name=":2">{{Cite journal |last1=Al Duhailib |first1=Zainab |last2=Farooqi |first2=Malik |last3=Piticaru |first3=Joshua |last4=Alhazzani |first4=Waleed |last5=Nair |first5=Parameswaran |date=May 2021 |title=The role of eosinophils in sepsis and acute respiratory distress syndrome: a scoping review |journal=Canadian Journal of Anesthesia |language=en |volume=68 |issue=5 |pages=715–726 |doi=10.1007/s12630-021-01920-8 |issn=0832-610X |pmc=7833890 |pmid=33495945}}</ref><ref>{{Cite web |last=Saini, MD |first=Sarbjit |date=30 Nov 2021 |title=Chronic spontaneous urticaria: Clinical manifestations, diagnosis, pathogenesis, and natural history |url=https://www.uptodate.com/contents/chronic-spontaneous-urticaria-clinical-manifestations-diagnosis-pathogenesis-and-natural-history?search=eosinopenia&source=search_result&selectedTitle=1~11&usage_type=default&display_rank=1 |access-date=2023-01-30 |website=UpToDate}}</ref><ref name=":4">{{Cite journal |last1=Shen |first1=M.-H. |last2=Qiu |first2=G.-Q. |last3=Wu |first3=X.-M. |last4=Dong |first4=M.-J. |date=2021 |title=Utility of the DECAF score for predicting survival of patients with COPD: a meta-analysis of diagnostic accuracy studies |url=https://doi.org/10.26355/eurrev_202106_26045 |journal=European Review for Medical and Pharmacological Sciences |volume=25 |issue=11 |pages=4037–4050 |doi=10.26355/eurrev_202106_26045 |pmid=34156682 |issn=1128-3602}}</ref> Other definitions include less than 10 cells/μLiter, while some clinical laboratories classify 0 cells/μLiter as within the acceptable range.<ref name=":6" /> The diagnosis of eosinopenia is challenging due to the low number of eosinophils normally present in blood and the fluctuations in eosinophil levels throughout the day.<ref name=":02" /><ref name=":3" />
== Causes == Eosinopenia is associated with several disease states and conditions, including inflammation and sepsis, endogenous catecholamines, and use of glucocorticoids.<ref name=":02" /> There are also medications that deliberately target eosinophils in order to treat eosinophil-mediated diseases, causing drug-induced eosinopenia.<ref name=":7">{{Cite journal |last1=Lindsley |first1=Andrew W. |last2=Schwartz |first2=Justin T. |last3=Rothenberg |first3=Marc E. |date=July 2020 |title=Eosinophil responses during COVID-19 infections and coronavirus vaccination |journal=Journal of Allergy and Clinical Immunology |language=en |volume=146 |issue=1 |pages=1–7 |doi=10.1016/j.jaci.2020.04.021 |pmc=7194727 |pmid=32344056}}</ref>
=== Catecholamines === Unlike other granulocytes, eosinophil count decreases in response to release of catecholamines.<ref name=":02" /> A hypothesized mechanism contributing to this change is decreased eosinophil production by the bone marrow in response to catecholamines. Epinephrine is also believed to stimulate receptors through the β-adrenergic pathway to decrease eosinophils in peripheral blood.<ref name=":02" />
=== Glucocorticoids === Use of glucocorticoids has been known to affect several blood components, including decreasing eosinophils.<ref name=":02" /> This cause of this effect is multifactorial. Glucocorticoids decrease the number of eosinophils in the circulation by causing them to exit the bloodstream and move into the tissue. The number of eosinophils released by the bone marrow is suppressed by glucocorticoids. It has also been theorized that glucocorticoids eliminate eosinophils in the blood by causing them to undergo apoptosis.<ref name=":02" />
=== Eosinophil-depleting medications === Due to the harmful role of eosinophils in diseases such as eosinophilic asthma and eosinophilic granulomatosis with polyangiitis, drugs have been developed to purposefully diminish eosinophils in order to alleviate symptoms.<ref name=":7" /> Some examples of these drugs include mepolizumab, reslizumab, and benralizumab.<ref>{{Cite journal |last1=Agache |first1=Ioana |last2=Beltran |first2=Jessica |last3=Akdis |first3=Cezmi |last4=Akdis |first4=Mubeccel |last5=Canelo‐Aybar |first5=Carlos |last6=Canonica |first6=Giorgio Walter |last7=Casale |first7=Thomas |last8=Chivato |first8=Tomas |last9=Corren |first9=Jonathan |last10=Del Giacco |first10=Stefano |last11=Eiwegger |first11=Thomas |last12=Firinu |first12=Davide |last13=Gern |first13=James E. |last14=Hamelmann |first14=Eckard |last15=Hanania |first15=Nicola |date=May 2020 |title=Efficacy and safety of treatment with biologicals (benralizumab, dupilumab, mepolizumab, omalizumab and reslizumab) for severe eosinophilic asthma. A systematic review for the EAACI Guidelines ‐ recommendations on the use of biologicals in severe asthma |url=https://onlinelibrary.wiley.com/doi/10.1111/all.14221 |journal=Allergy |language=en |volume=75 |issue=5 |pages=1023–1042 |doi=10.1111/all.14221 |pmid=32034960 |hdl=10468/9742 |s2cid=211064237 |issn=0105-4538|doi-access=free |hdl-access=free }}</ref>
== Role in inflammation and sepsis ==
=== Pathomechanism === Although eosinopenia has long been recognized as a laboratory marker for infection, the mechanism for this phenomenon is currently unknown.<ref name=":1" /><ref name=":8">{{Cite journal |last1=Lin |first1=Yao |last2=Rong |first2=Jiabing |last3=Zhang |first3=Zhaocai |date=24 May 2021 |title=Silent existence of eosinopenia in sepsis: a systematic review and meta-analysis |journal=BMC Infectious Diseases |language=en |volume=21 |issue=1 |pages=471 |doi=10.1186/s12879-021-06150-3 |issn=1471-2334 |pmc=8142617 |pmid=34030641 |doi-access=free }}</ref> One potential explanation is that eosinopenia may be an indication of immune dysregulation.<ref name=":2" /> In the body's response to a pathogen, the immune system activates "type 1 inflammation" which mobilizes certain immune cells to clear pathogens. This response can produce collateral damage of host tissue. To balance this, eosinophils are one component of "type 2 inflammation" that can begin to mend the tissue. As a result, eosinopenia may be a sign that the body has not mounted an appropriate type 2 inflammation response, so it may be doing more damage than normal to surrounding tissue.<ref name=":2" /> Another theory postulates that eosinophils in sepsis travel out of the blood and may contribute to tissue damage, causing relative eosinopenia in the blood with elevated eosinophils in affected tissue.<ref name=":2" /> Eosinophils have been shown to have a cytotoxic effect on bacteria, which contributes to surrounding tissue damage.<ref name=":1" /><ref name=":6" />
=== Clinical outcomes and diagnostic utility === Persistent eosinopenia in sepsis is independently associated with worse clinical outcomes, including increased mortality and increased rates of hospital readmission.<ref name=":2" /> It is unknown if eosinophils contribute directly to clearing pathogens in sepsis or if their absence is only an indicator that the immune system is dysregulated.<ref name=":2" /> The causative role of eosinopenia to poor survival in sepsis, if it exists, has yet to be established.<ref name=":2" />
The use of eosinopenia as a diagnostic tool in sepsis is debatable.<ref name=":8" /> Although there is a high incidence of eosinopenia in sepsis, it is not more effective as a biomarker than more commonly utilized indicators of sepsis, such as procalcitonin (PCT) and C-reactive protein (CRP).<ref name=":8" /> One advantage it does have compared these biomarkers is that it is generally a faster and cheaper test.<ref name=":8" />
== Role in COVID-19 ==
=== Disease course and risk stratification === Eosinopenia is a possible laboratory finding in patients who present with COVID-19 and is associated with disease severity, though it is not pathognomonic.<ref name=":6" /> One study found that 53% of patients admitted for COVID-19 had eosinopenia at time of admission; in another study of fatal COVID-19 cases, 81% of patients had eosinopenia.<ref name=":7" /> In patients with eosinopenia who present with COVID-19, eosinophil counts usually return to normal levels as they recover.<ref name=":6" /><ref name=":7" /> In fatal cases of COVID-19, eosinophil counts remain low for the duration of the disease.<ref name=":6" /> It is unclear if this eosinopenia contributes to the disease course.<ref name=":7" /> The presence of eosinopenia has been included in several risk stratification scores, such as the COVID-19-REAL score and PARIS score, which both use different definitions of eosinopenia as part of several factors to screen for COVID-19.<ref name=":6" /> Eosinopenia has also been proposed as a marker for distinguishing COVID-19 from influenza virus infection, since patients diagnosed with COVID-19 have slightly lower eosinophil counts than patients diagnosed with influenza.<ref name=":6" />
=== Pathomechanism === Though the most widely known role of eosinophils is in regards to allergy and parasitic infections, recent research has found evidence for an antiviral function of eosinophils.<ref name=":6" /><ref name=":7" /> Research has shown that mice that were genetically modified to have more eosinophils than normal were able to combat RSV infection more effectively than normal mice, while genetically eosinophil-depleted mice were less effective.<ref name=":7" /> The precise mechanism for this function is undetermined, though some elements of the eosinophil response to viruses include nitric oxide production and inactivation of viruses.<ref name=":6" /><ref name=":7" /> Though there is early research on the role of eosinophils in response to respiratory viruses, this function is still uncertain and requires additional research in order to define the extent to which eosinophils participate in antiviral immune response as well as clinical relevancy.<ref name=":7" />
The cause of eosinopenia in COVID-19 infection is also unknown at this time. Some proposed contributory mechanisms include increased movement of eosinophils out of the blood into tissue, decreased generation or output of eosinophils from the bone barrow, and shorter lifespan within the blood.<ref name=":6" /> One aspect of severe COVID-19 that may contribute to eosinopenia is the cytokine storm. In this disorder, cytokines may interact with eosinophils and modulate their activity, movement, or survival.<ref name=":6" />
==See also== * Eosinophilia * Hypereosinophilia
==References== {{reflist}}
==Further reading== * {{cite journal |vauthors=Krause JR, Boggs DR |title=Search for eosinopenia in hospitalized patients with normal blood leukocyte concentration |journal=Am. J. Hematol. |volume=24 |issue=1 |pages=55–63 |year=1987 |pmid=3799595 |doi=10.1002/ajh.2830240108|s2cid=20021710 }}
== External links == {{Medical resources | DiseasesDB = | ICD10 = D72.8 | ICD9 = {{ICD9|288.0}} | ICDO = | OMIM = | MedlinePlus = | eMedicineSubj = | eMedicineTopic = | MeshID = }} {{Monocyte and granulocyte disease}}
Category:Monocyte and granulocyte disorders