What is eosinophils in blood test
Last updated: April 1, 2026
Key Facts
- Eosinophils are granulocytes produced in bone marrow that represent 1-4% of total white blood cells in healthy individuals
- Elevated eosinophil levels (eosinophilia) may indicate allergies, parasitic infections, asthma, fungal infections, or certain autoimmune conditions
- Eosinophil counts are measured either as a percentage of white blood cells or as an absolute count (cells per microliter)
- An absolute eosinophil count above 500 cells per microliter is generally considered elevated and warrants further investigation
- Eosinophil levels can fluctuate based on time of day, stress, medications, and underlying health conditions
Overview
Eosinophils are specialized white blood cells that play a crucial role in immune response, particularly in combating parasitic infections and allergic reactions. When doctors request a complete blood count (CBC) test, they measure eosinophil levels to assess immune function and detect underlying health conditions.
Normal Eosinophil Ranges
In a healthy adult, eosinophils typically comprise 1-4% of total white blood cells. When expressed as an absolute count, normal levels range from 0 to 500 cells per microliter of blood. However, these reference ranges can vary slightly between laboratories depending on their testing methods and population data.
What Elevated Eosinophils Indicate
Elevated eosinophil counts (eosinophilia) may suggest several conditions:
- Allergic reactions including allergic asthma and seasonal allergies
- Parasitic infections such as hookworms, roundworms, or tapeworms
- Fungal infections and certain bacterial infections
- Autoimmune disorders like celiac disease and lupus
- Leukemia and lymphomas in certain cases
- Medications including some antibiotics and anti-inflammatory drugs
Low Eosinophil Counts
While less common, low eosinophil counts (eosinopenia) may result from steroid use, acute bacterial infections, or bone marrow disorders. Doctors investigate both elevated and depressed eosinophil levels in context with other test results and clinical symptoms.
Testing and Interpretation
Eosinophil counts are obtained through standard blood tests, particularly the complete blood count (CBC) with differential. Additional testing such as allergy tests, parasitic screenings, or imaging may be necessary depending on eosinophil levels and clinical presentation. Healthcare providers interpret results in conjunction with symptoms, medical history, and other laboratory values.
Related Questions
What does a high eosinophil count mean?
A high eosinophil count (above 500 cells/microliter) typically suggests allergies, parasitic infections, fungal infections, or autoimmune conditions. Your doctor will investigate the cause based on your symptoms and additional test results.
Can medications affect eosinophil levels?
Yes, certain medications can increase or decrease eosinophil counts. Steroids typically lower eosinophils, while some antibiotics and anti-inflammatory medications can raise them. Inform your doctor about all medications when discussing test results.
How often should eosinophil levels be checked?
Eosinophil levels are typically checked as part of routine blood work or when your doctor suspects an allergic reaction, infection, or immune disorder. Frequency of testing depends on your condition and treatment plan.
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Sources
- MedlinePlus - White Blood Cell Differential CC0-1.0
- Wikipedia - Eosinophil CC-BY-SA-4.0