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Basophils (Absolute)

The number of basophils, the rarest white blood cell, in each microliter of your blood. Basophils take part in allergic reactions.

AI-drafted. Awaiting verificationAlso called BASO#LOINC 704-7

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What it is

Basophils are the least common type of white blood cell, usually fewer than 2 out of every 100. They hold histamine and other chemicals that play a part in allergic reactions and inflammation. This test counts how many basophils are in a set amount of blood, as part of the white blood cell differential in a CBC. Because basophils are so rare, many results are 0.0 or 0.1 ×10³/µL, and rounding to one decimal can make small changes look big.

Why it matters

The basophil count adds detail to a white blood cell differential. A mildly high count can happen with allergic reactions or ongoing inflammation. A count that stays high on repeat tests, especially together with other blood count changes, may lead your clinician to look more closely for the cause. A low or zero count is normal for many people and rarely means anything on its own.

If it’s low

A low or zero basophil count is normal for most people. The usual range starts at or near zero, and automated machines tend to read basophils on the low side. Steroid medicines, an acute infection or a severe injury can lower the count for a while. A low result on its own rarely points to a problem.

Common causes

  • Normal variation, since many healthy people have 0.0
  • Steroid medicines (corticosteroids)
  • Acute infection or severe injury
  • Active chronic hives (urticaria) in some people

What can help

  • Tell your clinician about any steroid medicines you take by mouth or injection

If it’s high

A high basophil count is called basophilia. Labs set the upper limit between about 0.1 and 0.2 ×10³/µL, and a single slightly high result is common and often has no clear cause. Allergic reactions, long-lasting inflammation and some infections can raise basophils. Less often, a count that stays high is linked to bone marrow conditions called myeloproliferative neoplasms, which usually also change other blood counts. Your clinician can put the number in context and decide whether to repeat it.

Common causes

  • Allergic reactions, including reactions to food or medicines
  • Long-lasting inflammation, such as inflammatory bowel disease or autoimmune disease
  • Some infections, such as influenza and tuberculosis
  • Bone marrow conditions such as chronic myeloid leukemia, polycythemia vera or essential thrombocythemia (uncommon)

What can help

  • Share your allergy history, recent illnesses and medicines with your clinician
  • Ask whether a repeat CBC, or a look at your blood smear under the microscope, would help
  • Keep the range and any flag printed on your lab report, since ranges differ between labs

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

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

What can affect your result

  • Method: automated analyzers read basophils less accurately than other white cells, and a microscope count can differ
  • Steroid medicines, which can lower the count
  • Allergic reactions and active hives, which can change it
  • Age: babies and children have higher upper limits than adults
  • Rounding: results printed to one decimal place, such as 0.0 or 0.1, hide small differences
  • Your lab's range: upper limits differ between labs, from about 0.1 to 0.2 ×10³/µL
  • Automated analyzers count basophils less accurately than other white cells and tend to read low. The reference method is a microscope count of 400 white cells.
  • Automated and microscope basophil counts can agree poorly, especially when counts are very low.
  • Steroid medicines (corticosteroids) lowered basophil counts in healthy volunteers.
  • Many labs print only one decimal place, so small differences between 0.0 and 0.1 are hidden.

No clear time-of-day pattern between 8 am and 8 pm in a small study of 10 healthy adults. Varies with the cause; the count can change within days with steroid medicines and over longer periods with ongoing inflammation.

When to talk to a clinician

Talk with your clinician if a high basophil count shows up again on a repeat test, or if it comes with other blood count changes, fever, night sweats, unexplained weight loss, ongoing tiredness or a feeling of fullness in the upper left belly. Call 911 or your local emergency number for trouble breathing, swelling of the face or throat, chest pain or fainting.

Questions you could ask

  • What is my lab's range for basophils, and was anything flagged?
  • Could allergies or long-lasting inflammation explain this result?
  • Should we repeat the count, and would a blood smear review help?
  • Do my other blood counts add anything to the picture?
  • Is a low or zero basophil count expected with my lab's method?
  • Do any of my medicines, such as steroids, affect this result?

Questions people ask

What is a normal basophil count?

Basophils are the rarest white cell, so most healthy results are 0.0 to 0.1 ×10³/µL. Labs list an upper limit between about 0.1 and 0.2, so compare your result with the range on your own report.

My lab says 0.0. Is that a problem?

Usually not. The usual range starts at zero, basophils are very rare, and many labs round to one decimal. Automated machines also tend to under-read basophils.

What can raise my basophil count?

Allergic reactions, long-lasting inflammation and some infections can. A single slightly high result is common and is often just repeated. A count that stays high, especially with other blood count changes, is something your clinician may look into further.

Why do labs list different basophil ranges?

Basophils are so rare that methods, rounding and the group of healthy people used to set the range all matter. For example, Mayo lists 0.01 to 0.08 for adults while Labcorp lists 0.0 to 0.2. Your own lab's range is the one to use.

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

×10³/µL and ×10⁹/L are the same number. To get cells/µL, multiply by 1,000, so 0.1 ×10³/µL is 100 cells/µL.

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 Basophils (abs) unit converter

Is a change real?

Basophils (abs) naturally varies about 11.34% from test to test in the same healthy person. Between two results from the same lab, a change of roughly 35% 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

Basophils are the least numerous circulating granulocytes. Their granules hold histamine and heparin, IgE binds to their surface, and IL-3 is their main growth factor; maturation in the marrow takes about 7 days. The CLSI reference method is a manual differential of 400 leukocytes on a stained smear. Automated analyzers combine impedance (the Coulter principle) with flow cytometry, but basophil counts are the least accurate of the five-part differential and tend to underestimate, and in a small study of healthy volunteers manual and automated counts agreed poorly (mean manual count about 43 cells/µL). Reference upper limits therefore vary by method and population, from 0.08 ×10⁹/L (Mayo, adults) through 0.1 (ARUP, Manchester) to 0.2 (Labcorp, NSW Health Pathology). StatPearls describes basophilia as an absolute count above about 200 cells/µL and notes that cutoffs differ by lab. Unexplained persistent basophilia, especially with left-shifted neutrophilia or circulating blasts, prompts smear review and evaluation for a myeloproliferative neoplasm, including BCR-ABL1 testing for chronic myeloid leukemia. Basophil counts fell on prednisolone in healthy volunteers and are reduced in active chronic urticaria, where cells are thought to be recruited into wheals.

LOINC 704-7 (primary), 705-4, 26444-0. Specimen: whole-blood.

Sources

  1. Pediatric Testing Reference Ranges (test 005009, CBC With Differential/Platelet), Labcorp Diagnostics
  2. Sample patient report, test 005013 (CBC with Diff, Platelet, NLR), Labcorp
  3. NSW Health Pathology: Adult Reference Intervals (CPROAH Reference Ranges Adult), NSW Health Pathology (2019)
  4. CBC with Platelet Count and Automated Differential (test 0040003), hotline effective March 1, 2021: reference intervals, ARUP Laboratories (2021)
  5. Haematology User Guide: Blood counts reference ranges, Manchester University NHS Foundation Trust (2024)
  6. Complete Blood Cell Count (CBC) with Differential, Blood (test ID CBC): reference values, Mayo Clinic Laboratories
  7. Normal Values for Leukocyte Concentration in Blood (Table 63-1), Harrison's Principles of Internal Medicine, 19th edition (McGraw-Hill) (2015)
  8. Basophilia, StatPearls (NCBI Bookshelf) (2024)
  9. 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)
  10. Blood differential test, MedlinePlus Medical Encyclopedia (National Library of Medicine) (2025)

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

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