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Eosinophils
The cells of allergic reactions and anti-parasite defense. Rise in allergy, asthma, helminth infections and some skin diseases.
Other names: Eosinophils, EOSSection: Blood cells
Updated: August 31, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortEosinophils are the cells of allergic reactions and anti-parasite defense. A typical share is 1–4% of all leukocytes. Growth most often points to allergy, asthma or helminths; a fall occurs with steroids and acute stress.
Reference ranges
Group
Reference range
Share of all leukocytes
1–4%
The source gives 1–4% of all white blood cells. The source gives this share of all white blood cells; many labs also report absolute counts. Reference ranges vary between laboratories and assays — use the range printed on your own lab report.
Check your value
Enter the number from your lab report — see how it compares with the typical range. Mind the units shown in the chosen row.
A rough comparison with a typical range, not a diagnosis. Reference ranges vary between laboratories — check the range on your own report and let a clinician interpret the result.
What this marker is
Eosinophils are a small leukocyte population specializing in allergic reactions and defense against parasites: they release substances that destroy helminths and drive inflammation in asthma and atopy. The report shows their percentage of all leukocytes.
Raised eosinophils (eosinophilia) is one of the most 'telling' formula shifts: behind it usually lies allergy (hay fever, atopic dermatitis, food reactions), bronchial asthma or a helminth infection. Marked, persistent eosinophilia is rare and calls for deeper workup.
When it is high
Allergic diseasesHay fever, atopic dermatitis, hives, food allergy — the most common causes.
Bronchial asthmaEosinophilic airway inflammation is mirrored by raised blood eosinophils.
Helminth and parasite infectionsAscariasis, giardiasis, echinococcosis — classic causes of eosinophilia.
Drug reactionsAntibiotics and some other medicines can cause eosinophilia as a side effect.
Blood disordersHypereosinophilic syndrome and some leukemias — rare causes of marked growth.
When it is low
GlucocorticoidsSteroids quickly lower eosinophils — an expected effect.
Acute stress and acute infectionsIn the acute phase of bacterial inflammation eosinophils can temporarily vanish from blood.
Cushing's syndromeExcess of the body's own adrenal hormones suppresses eosinophils.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Daily rhythm (higher at night)GlucocorticoidsAllergy season
How to prepare
Taken within a morning fasting CBC with differential. The level has a daily rhythm (higher at night and early morning) — retest at the same time. Tell your doctor about your medicines: steroids markedly affect the result.
When a retest makes sense
For a moderate rise — in 2–4 weeks at the same time of day; during allergy or parasite treatment — on the doctor's schedule.
Who usually reviews this result
A result outside the reference range is usually reviewed by: GP or pediatrician; eosinophilia — allergist-immunologist, parasitologist or hematologist. Bring your lab report and any previous results to the appointment.
Names used on lab reports
Your report may use any of these names: EosinophilsEOS
Units
Measured in: % of white blood cells
Several markers on your report?
See how MedProtect explains results in the app: the whole report, a check of the recognized values, and a clear breakdown.
Possibly, but not necessarily: a modest rise occurs outside allergy too. The doctor will match the result with complaints (itching, rash, seasonal congestion) and order allergy testing if needed.
Do eosinophils find worms?
Eosinophilia is an indirect sign of parasitosis, not proof: the diagnosis is confirmed by stool tests and specific assays. Normal eosinophils do not rule out helminths either.
Why are my eosinophils zero?
With stress, acute infection or steroids, eosinophils can temporarily be undetectable — usually not a problem by itself. If zero persists without a reason, show the result to your GP.
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