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Eosinophil count (serum/plasma concentration)

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

This test measures the concentration of eosinophils, a type of white blood cell involved in allergic reactions and parasitic infections.

Quick summary

["Eosinophils help identify certain immune responses and conditions."]

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

Key facts at a glance

LOINC
43431-6
Short code
E coli K1 Ag Ser Ql
Synonyms
E coli K1 Ag Ser Ql
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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

What Is an Eosinophil?

Eosinophils are a type of white blood cell that plays a role in defending the body against parasites and managing allergic reactions. They release chemicals that help fight off certain infections and control inflammation. Elevated levels may suggest allergies, asthma, parasitic infections, or other immune-related conditions.

Why Might This Test Be Ordered?

Your healthcare provider may order this test if you have symptoms like persistent itching, skin rashes, asthma, or unexplained allergies. It could also be part of a broader evaluation for conditions like eosinophilic esophagitis, certain cancers, or autoimmune disorders.

What Does the Result Mean?

Results are not provided with specific reference ranges in this generic format. Elevated eosinophil levels may indicate an allergic reaction, parasitic infection, or other immune-related issues. Lower-than-normal levels might suggest certain infections or immune deficiencies. Always discuss results with your doctor.

How Is This Test Performed?

A blood sample is drawn, typically from a vein in your arm. The blood is then processed to measure the concentration of eosinophils in the serum or plasma.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Eosinophil Level (Serum/Plasma)

Frequently asked questions

What conditions or symptoms might this test help diagnose?
Elevated eosinophil counts can signal conditions such as allergic disorders (e.g., asthma, eczema), parasitic infections, certain cancers (e.g., leukemia), or inflammatory diseases. Low levels may be associated with viral infections or certain immune deficiencies. This test is often used as part of a broader diagnostic evaluation.
How soon will I get my results?
Results are usually available within 1 to 3 business days, depending on your lab. Your healthcare provider will explain the findings and next steps during your follow-up visit.
Can I fast before this test?
No fasting is required for this test. Blood is drawn at any time of day, and it does not affect the accuracy of the results.
  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