Eosinophils

Overview

Eosinophils measure the absolute count or percentage of a type of white blood cell involved in allergic responses, parasitic infections, and immune regulation. These granulocytes release cytotoxic granules containing major basic protein, eosinophil cationic protein, and other mediators that target parasites and modulate inflammation. Elevated levels (eosinophilia) indicate allergic disorders, parasitic infections, drug reactions, or hypereosinophilic syndromes, while low levels (eosinopenia) occur with acute infections, stress, or corticosteroid use. Clinically, eosinophil counts help diagnose and monitor allergic, parasitic, and certain hematologic conditions.

Clinical Use Cases

  • Diagnosing allergic diseases (asthma, allergic rhinitis, atopic dermatitis).
  • Evaluating parasitic infections (helminths, tissue-invasive protozoa).
  • Assessing drug hypersensitivity reactions and eosinophilic organ disorders.
  • Monitoring hypereosinophilic syndromes and Churg-Strauss vasculitis.

Specimen Types

  • Whole blood (EDTA or heparin).
  • Bone marrow (aspirate/biopsy in specialized cases).

Measurement Methods

  • Automated hematology analyzer differential count.
  • Manual microscopic differential on Wright-Giemsa stained blood smear.
  • Flow cytometry for immunophenotyping in research.

Test Preparation and Influencing Factors

  • No fasting required.
  • Corticosteroids and high-dose epinephrine suppress eosinophil counts.
  • Pregnancy and estrogen therapy may elevate levels.
  • Recent infection, exercise, or diurnal variation (morning peak) influence results.

Synonyms

  • Eos.
  • Absolute eosinophil count (AEC).
  • Eosinophil percentage.

Further Reading

  • Eosinophil count – absolute; MedlinePlus;