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What are eosinophils and the causes for count changes

Eosinophils are a type of blood cell that originate from the differentiation of a cell produced in the bone marrow, the myeloblast, and aims to defend the organism against the invasion of foreign microorganisms, being very important for immune system function.

These defense cells are present in the blood at high concentrations mainly during allergic reactions or in case of parasitic, bacterial and fungal infections. Eosinophils are usually in lower blood concentrations than other body defense cells, such as lymphocytes, monocytes or neutrophils, which also work in the immune system.

What are eosinophils and the causes for count changes

Reference ranges

The amount of eosinophils in the blood is evaluated in a leukogram, which is a part of the hemogram in which the white cells of the organism are evaluated. Normal values of eosinophil in the blood are:

  • Absolute value: 40 to 500 cells / μL of blood - is the total eosinophil count in the blood;
  • Relative value: 1 to 5% - is the percentage of eosinophils compared to other leukogram cells.

The values may change slightly according to the laboratory in which the test is performed and therefore the reference range should also be checked in the examination itself.

What may cause changes in the Eosinophils

When the amount of eosinophils of the test is outside the normal range, it is considered that the person may have increased or decreased eosinophils, each type of alteration has different causes.

1. High Eosinophils

When the blood eosinophil count is greater than the normal reference range, it is called eosinophilia. The main causes of eosinophilia are:

  • Allergy, such as asthma, urticaria, allergic rhinitis, dermatitis, eczema;
  • Parasitosis by worms, such as ascaridiasis, toxocariasis, ancylostomiasis, oxyuriasis, schistosomiasis, among others;
  • Infections, such as typhoid fever, tuberculosis, aspergillosis, coccidioidomycosis, some viruses;
  • Allergy to the use of medication, such as ASA, antibiotics, antihypertensives or tryptophan, for example;
  • Inflammatory skin diseases such as bullous pemphigus, dermatitis;
  • Other inflammatory diseases such as inflammatory bowel disease, hematological diseases, cancer or genetic diseases that cause hereditary eosinophilia, for example.

In som​​​e rare cases, it is still possible that you cannot find the cause of eosinophil increase, in these cases it is called idiopathic eosinophilia. There is also called hypereosinophilia, which is when the eosinophil count is very high and exceeds 10,000 cells / μL, being more common in autoimmune and genetic diseases, such as hypereosinophilic syndrome.

How to know if your eosinophil count is above average

A person who has high eosinophils does not always have symptoms, but they can arise from the very disease that caused eosinophilia, such as shortness of breath in cases of asthma, sneezing and nose congestion in case of allergic rhinitis or abdominal pain in cases of infections parasitic diseases, for example.

For people with hereditary hypereosinophilia, it is possible that excess eosinophils cause symptoms such as pain in the belly, itchy skin, fever, body aches, abdominal cramps, diarrhea and nausea.

What are eosinophils and the causes for count changes
Eosinophil in a blood sample
Eosinophil in a blood sample

2. Low Eosinophils

A Low eosinophil count, is called eosinopenia, and occurs when eosinophils are below 40 cells / μL and can reach 0 cells / μL.

Eosinopenia can occur in cases of acute bacterial infections, such as pneumonia or meningitis, for example, since they are serious bacterial infections that usually increase other types of defense cells, such as neutrophils, which can decrease the absolute or relative count of eosinophils. The reduction of eosinophils may also be a result of decreased immunity due to an illness or use of drugs that alter the functioning of the immune system, such as corticosteroids.

In addition, it is possible to have low eosinophils without any changes. This situation may also arise during pregnancy, when a physiological reduction in eosinophil counts occurs.

Other rare causes of eosinopenia include autoimmune diseases, bone marrow diseases, cancer or HTLV, for example.

How to know if your eosinophil count is below average

Low eosinophil count usually does not cause symptoms, unless it is associated with a disease that may present some type of clinical manifestation.

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