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Eosinophil count (peripheral blood)

Published: August 9, 2026Updated: August 16, 2026

This test measures the number of eosinophils, a type of white blood cell, in your blood. Eosinophils help fight infections and respond to allergies and inflammation.

Quick summary

["Eosinophils help protect your body from harmful substances and infections."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
20820-7
Short code
Deprecated E coli K99 TSMI Ql Aggl
Synonyms
Deprecated E coli K99 TSMI Ql Aggl
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
aggl
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Might You Need This Test?

Your doctor may order this test to check for conditions like allergies, asthma, parasitic infections, or certain types of cancer. It can also help diagnose or monitor conditions such as eosinophilic esophagitis, inflammatory bowel disease, or reactions to medications.

What Does It Measure?

Eosinophils are a type of immune cell that increases in response to allergies, infections, or inflammation. High levels may suggest an allergic reaction, parasitic infection, or autoimmune disorder.

How Is the Test Done?

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab, where it is analyzed to count the number of eosinophils.

What Are Common Results?

Results are typically reported as the absolute count of eosinophils per microliter (µL) of blood. While reference ranges vary by lab, elevated counts (above normal) may indicate certain conditions, while normal or low counts may suggest other health considerations.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance: Eosinophils play a key role in immune responses. Elevated eosinophil counts can signal allergic reactions, parasitic infections, asthma, or certain cancers. Low counts may indicate immune suppression or other systemic conditions. Always discuss results with your healthcare provider for personalized interpretation.

Short name

Eosinophil CBC

Frequently asked questions

What causes eosinophil levels to be high?
High eosinophil levels can be caused by allergies, asthma, parasitic infections, certain cancers (like lymphoma or leukemia), autoimmune diseases, or reactions to medications.
What does it mean if my eosinophil count is low?
Low eosinophil counts may indicate immune suppression, certain infections, or conditions affecting white blood cell production. This can sometimes be due to medications or underlying health issues.
How often should I get this test?
Your doctor will determine how often you need this test based on your symptoms, medical history, and ongoing health needs. Regular monitoring may be recommended if you have conditions like allergies or chronic inflammation.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy