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Eosinophil count in serum/plasma (absolute)

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 caused by parasites and play a role in allergic reactions and certain inflammatory conditions.

Quick summary

["Eosinophil levels can help diagnose or monitor conditions like allergies, asthma, parasitic infections, or certain autoimmune diseases."]

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

Key facts at a glance

LOINC
31810-5
Short code
E histolyt Ag Ser-aCnc
Synonyms
E histolyt Ag Ser-aCnc
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

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms such as persistent itching, skin rashes, asthma, chronic sinusitis, or unexplained weight loss. It may also be used to monitor conditions like eosinophilic esophagitis, certain cancers, or reactions to medications.

What to Expect Before the Test

No special preparation is needed for this test. You may have a blood draw at a clinic, hospital, or lab. If you’re taking blood thinners or have a history of bleeding disorders, let your provider know before the test.

How the Test Works

A small amount of blood is drawn from a vein in your arm. The blood is then processed to count the number of eosinophils, a type of white blood cell, using a specialized blood test machine.

What the Results Mean

Results are typically reported as the absolute number of eosinophils per microliter (µL) of blood. High levels may indicate allergic reactions, infections, or inflammatory conditions, while low levels may suggest immune suppression or certain blood disorders.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Eosinophil count

Frequently asked questions

What Does an Elevated Eosinophil Count Indicate?
An elevated eosinophil count can signal conditions such as allergies, asthma, parasitic infections, eosinophilic granulomatosis with polyangiitis (EGPA), or certain types of cancer like lymphoma. It may also appear in response to certain medications or autoimmune diseases.
What Does a Low Eosinophil Count Indicate?
Low eosinophil counts may suggest immune suppression, certain blood disorders, or long-term use of corticosteroids. It can also occur in people with severe infections or certain genetic conditions.
How Often Should I Get This Test?
The frequency of this test depends on your medical condition and treatment plan. Your healthcare provider will determine how often to check your eosinophil levels based on your symptoms, diagnosis, or ongoing treatment.
  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