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Eosinophils (Absolute)

The number of eosinophils, white blood cells that take part in allergies and fight some parasites, in each microliter of your blood.

AI-drafted. Awaiting verificationAlso called AEC, TEC, EO#LOINC 711-2

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What it is

Eosinophils are a type of white blood cell made in your bone marrow. They help your body deal with some parasites and take part in allergic reactions, such as hay fever, asthma and eczema. This test counts how many eosinophils are in a set amount of blood. It is part of the white blood cell differential in a complete blood count (CBC), and it is also called the absolute eosinophil count, or AEC. Most people have only a small number, and many results fall between 0.0 and 0.5 ×10³/µL.

Why it matters

Eosinophil counts help clinicians understand allergic and inflammatory conditions, reactions to medicines, and some infections. A mildly high count is common and often has a simple cause, such as seasonal allergies or asthma. Clinicians look at the number, how it changes over time, and your symptoms together. Rarely, a very high count that lasts can affect organs such as the heart, lungs or skin, which is why a lasting high result is followed up.

If it’s low

A low or zero count is common and is usually not a concern. The usual range starts at or near zero, so a result of 0.0 is often simply normal. Counts can drop while you take steroid medicines or when the body makes too much cortisol. A low count rarely points to a problem by itself, so clinicians usually read it alongside your other results.

Common causes

  • Normal variation, since zero is a common result
  • Time of day, because counts run lowest in the morning
  • Steroid medicines (corticosteroids)
  • High natural cortisol levels, such as with Cushing syndrome
  • Alcohol intoxication

What can help

  • Tell your clinician about any steroid medicines you take by mouth or injection, since they lower this count

If it’s high

A high count is called eosinophilia. Guidelines use a cutoff of more than 0.5 ×10³/µL (500 cells/µL) and describe mild, moderate and severe levels. Many people with a mildly high count have allergies, asthma, eczema or a reaction to a medicine. Other causes include parasite infections, some digestive and skin conditions, low cortisol from the adrenal glands, and, less often, immune or blood disorders. One result cannot tell you which cause is behind it. Your clinician will look at your symptoms, medicines, travel history and any repeat counts.

Common causes

  • Allergies, such as hay fever, and allergic asthma
  • Eczema and other allergic skin conditions
  • A reaction to a medicine (for example some antibiotics, anti-inflammatory pain relievers, anti-seizure medicines or allopurinol)
  • Parasite infections, mostly in people who have lived in or traveled to certain parts of the world
  • Eosinophilic conditions of the esophagus or bowel
  • Low cortisol from adrenal gland problems
  • Autoimmune and inflammatory diseases
  • Some blood disorders and cancers, such as lymphoma or leukemia (uncommon)

What can help

  • Bring a list of your medicines, supplements and recent travel to your visit
  • Ask whether allergies or asthma could explain the result, and how to manage them if so
  • Ask whether a repeat count makes sense, since that is how clinicians tell a one-time rise from a lasting one
  • Talk with your clinician before changing any medicine you take

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 3 ranges

See Eosinophils (abs) by age and sex, with the U.S. survey numbers where they exist.

Eosinophilia categories (French 2023 guideline, adapted from Valent et al.; StatPearls severity grades)

  • Not eosinophilia (0.50 or below)below 0.51 ×10³/µL
  • Mild eosinophilia (above 0.5 to 1.5)0.51 to under 1.51 ×10³/µL
  • Moderate eosinophilia (above 1.5 to 5.0; called hypereosinophilia if still above 1.5 on a repeat count about a month later)1.51 to under 5.01 ×10³/µL
  • Severe eosinophilia (above 5.0)5.01 and above ×10³/µL

If this applies to you

Eosinophils (abs) means a little more for some people. Open the one that fits you.

Taking methotrexate

Eosinophils are white cells often linked to allergies, and they are counted as part of the full blood count. The BSR lists an unexplained rise in eosinophils among the results that should prompt an urgent call to the rheumatology team.

Blood tests on methotrexate

How common is your level?

NHANES describes the US civilian, non-institutionalized population, not a 'healthy' reference group. People with disease, on medication, fasting or not (except fasting-subsample markers), smokers and so on are all included. A percentile says where a value sits among Americans of that sex and age, not whether it is normal.

How Eosinophils (abs) varies with age in the U.S.Shaded: middle 90% and middle 50% of people. Line: the median. ×10³/µL. Point at any age, or focus the chart and use the arrow keys, to read both sexes in words.

Use the left and right arrow keys to read each age. Shift moves five years.

Reference data derived from CDC/NCHS National Health and Nutrition Examination Survey (NHANES), cycles 2015-2016, 2017-March 2020 (pre-pandemic), August 2021-August 2023. Analysis by bloodtesttracker.com; not endorsed by CDC, NCHS or HHS.

Explore Eosinophils (abs) by age and sex: every percentile as a table, with a download.

What can affect your result

  • Time of day: counts are lowest in the morning and highest around midnight, though the swing is small
  • Steroid medicines, which lower the count within days
  • Allergy season and asthma flare-ups, which can raise it in people with allergies
  • Some medicines, including certain antibiotics, anti-seizure medicines and anti-inflammatory pain relievers
  • Living in or traveling to areas where parasite infections are common
  • Age: babies and young children have higher ranges than adults
  • Your lab's method and range: upper limits differ between labs, from about 0.4 to 0.5 ×10³/µL
  • Steroid medicines (corticosteroids) lower the eosinophil count within days, so a result taken during or after steroid treatment can look lower than it otherwise would.
  • Some medicines can raise the count, including certain antibiotics, anti-seizure medicines, anti-inflammatory pain relievers and allopurinol.
  • High natural cortisol levels (for example in Cushing syndrome) and alcohol intoxication are linked to lower counts.
  • If the analyzer raises a flag, the lab may re-count on a stained blood smear under the microscope, and the two methods can differ slightly.

Eosinophil counts tend to be lowest in the morning and highest around midnight, so drawing at a similar time of day makes results easier to compare. Within days for steroid-related changes. Medicine-related eosinophilia can take up to about 6 months to settle after the cause is stopped.

When to talk to a clinician

Contact your clinician soon if your eosinophil count is above 1.5 ×10³/µL (1,500 cells/µL), especially if it was high on an earlier test too. Get prompt care for new shortness of breath, chest pain, a spreading rash, swelling, numbness or weakness along with a high count. Call 911 or your local emergency number for chest pain, trouble breathing, confusion or fainting.

Questions you could ask

  • What is my lab's range for eosinophils, and was anything flagged?
  • At what level would you want to follow up on this?
  • Could allergies, asthma or a medicine I take explain this result?
  • Should we repeat the count, and when?
  • Are any other tests worth considering based on my symptoms and travel history?
  • Do any of my medicines, such as steroids, affect this result?

Questions people ask

What is a normal eosinophil count?

Most labs list an upper limit of about 0.4 to 0.5 ×10³/µL (400 to 500 cells/µL) for adults, and the lower limit is at or near zero. Labs differ a little, so compare your result with the range printed on your own report.

My eosinophils are high. Does that mean I have an allergy or parasites?

Not necessarily. Allergies, asthma, eczema and medicine reactions are common reasons. Parasite infections matter mostly if you have lived in or traveled to certain regions. The count alone cannot tell the cause, so your clinician looks at your symptoms, medicines and history, and may repeat the test.

Why is my eosinophil count 0.0?

A zero or very low count is common and usually not a concern. The usual range starts at zero. Steroid medicines, high cortisol levels and a morning draw can all push the count lower.

How do I convert between ×10³/µL, ×10⁹/L and cells/µL?

×10³/µL and ×10⁹/L are the same number, so 0.5 in one is 0.5 in the other. To get cells/µL, multiply by 1,000, so 0.5 ×10³/µL is 500 cells/µL.

Is the eosinophil percent or the absolute count more useful?

The absolute count. The percent shifts when other white cells go up or down, even if the number of eosinophils has not changed. Eosinophilia is defined by the absolute count.

Show the science and sources

Units

  • 1 ×10³/µL = 1 ×10³/µL
  • 1 ×10³/µL = 1 ×10⁹/L
  • 1 ×10³/µL = 1000 cells/µL
  • 1 ×10³/µL = 1000 cells/mm³

Open the Eosinophils (abs) unit converter

Is a change real?

Eosinophils (abs) naturally varies about 14.38% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 45% or more is unlikely to be day-to-day noise or lab variation (95% reference change value). Source: Systematic review and meta-analysis of within-subject and between-subject biological variation estimates of 20 haematological parameters (Coskun A et al., EFLM WG-BV).

For clinicians and researchers

Eosinophils are granulocytes made in the bone marrow under the influence of IL-5, IL-3 and GM-CSF. They circulate with a half-life of about 4.5 to 8 hours and live in tissue, mostly the airways and gut, for about 8 to 12 days, so a blood count is a snapshot that can understate tissue eosinophilia (eosinophilic esophagitis in young people, for example, usually shows no or only mild blood eosinophilia). Automated analyzers classify eosinophils by flow cytometry and report both percent and absolute counts; analyzer flags can trigger a smear review. Absolute count equals percent times the total white cell count divided by 100. Mayo Clinic Laboratories (Sysmex XN analyzer) lists 0.03 to 0.48 ×10⁹/L for adults of both sexes and includes a Canadian Health Measures Survey reference-interval study among its references. Definitions use absolute counts: blood eosinophilia is 0.5 to 1.5 ×10⁹/L, hypereosinophilia is above 1.5 ×10⁹/L on two occasions at least a month apart and/or tissue eosinophilia, and hypereosinophilic syndrome additionally requires organ damage attributed to eosinophils with other causes excluded. Eosinophils follow a daily rhythm that rises through the day to a peak near midnight (amplitude about 0.04 ×10⁹/L in healthy young men). Corticosteroids lower the count within days (eosinophils fell in every subject after 3 days of prednisolone in one small study), and the French guideline lists failure of the count to normalize on systemic corticosteroids among features suggesting a clonal cause.

LOINC 711-2 (primary), 712-0, 26449-9. Specimen: whole-blood.

Sources

  1. CBC with Platelet Count and Automated Differential (test 0040003), hotline effective March 1, 2021: reference intervals, ARUP Laboratories (2021)
  2. Complete Blood Cell Count (CBC) with Differential, Blood (test ID CBC): reference values, Mayo Clinic Laboratories
  3. Sample patient report, test 005013 (CBC with Diff, Platelet, NLR), Labcorp
  4. Pediatric Testing Reference Ranges (test 005009, CBC With Differential/Platelet), Labcorp Diagnostics
  5. Haematology User Guide: Blood counts reference ranges, Manchester University NHS Foundation Trust (2024)
  6. NSW Health Pathology: Adult Reference Intervals (CPROAH Reference Ranges Adult), NSW Health Pathology (2019)
  7. Normal Values for Leukocyte Concentration in Blood (Table 63-1), Harrison's Principles of Internal Medicine, 19th edition (McGraw-Hill) (2015)
  8. Eosinophil count - absolute, MedlinePlus Medical Encyclopedia (National Library of Medicine) (2025)
  9. Eosinophilia, StatPearls (NCBI Bookshelf) (2023)
  10. French guidelines for the etiological workup of eosinophilia and the management of hypereosinophilic syndromes, Orphanet Journal of Rare Diseases (2023)
  11. Diurnal variation of hematology parameters in healthy young males: the Bispebjerg study of diurnal variations, Scandinavian Journal of Clinical and Laboratory Investigation (2011)
  12. Blood basophil numbers in chronic ordinary urticaria and healthy controls: diurnal variation, influence of loratadine and prednisolone and relationship to disease activity, Clinical and Experimental Allergy (2003)

AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.

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