Basophils (Percent)
The share of your white blood cells that are basophils, the rarest white cell type, which takes part in allergic reactions.
AI-verified against cited sources. Awaiting expert reviewAlso called BASO%LOINC 706-2
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What it is
Basophils are the least common white blood cell. They hold histamine and other chemicals that play a part in allergic reactions and inflammation. This result shows what percent of all your white blood cells are basophils, and it comes from the white blood cell differential in a CBC. Most results are under 2 percent. The percent also depends on the other white cell types, so clinicians usually rely on the absolute basophil count.
Why it matters
The percent gives a quick view of the mix of white blood cells. If it looks high, your clinician will usually check the absolute count, which is easier to compare between labs. Some labs, including Labcorp, do not set a range for the percent at all.
If it’s low
A low or zero percent is normal for many people, since basophils are so rare. A rise in other white cells, such as neutrophils during an infection, pushes the basophil share down. Steroid medicines, an acute infection or a severe injury can also 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 percent
- A rise in other white cells, such as neutrophils during an infection
- Steroid medicines (corticosteroids)
- Acute infection or severe injury
What can help
- Check the absolute basophil count and the total white blood cell count
- Tell your clinician about any steroid medicines you take by mouth or injection
If it’s high
A slightly high percent is common and often has no clear cause. It can reflect allergic reactions, long-lasting inflammation or some infections, and it can also look larger when other white cells are low. Check the absolute count. If that is within your lab's range, the high percent may just reflect fewer of the other cells. A basophil level that stays high on repeat tests, especially with other blood count changes, is something your clinician may look into.
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, tuberculosis and chickenpox
- Fewer neutrophils or lymphocytes than usual, which makes the basophil share look larger
- After the spleen has been removed
- Bone marrow conditions such as chronic myeloid leukemia (uncommon)
What can help
- Look at the absolute basophil count and your total white blood cell count alongside the percent
- Share your allergy history, recent illnesses and medicines with your clinician
- Ask whether a repeat CBC makes sense
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.
For adults: 0.3–1.4 %. Source: ARUP Laboratories, Harrison's Principles of Internal Medicine, 19th edition (McGraw-Hill), MedlinePlus Medical Encyclopedia (National Library of Medicine), Labcorp, StatPearls (NCBI Bookshelf), Clinical and Experimental Allergy.
See Basophils (%) 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.
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 (%) by age and sex: every percentile as a table, with a download.
What can affect your result
- Changes in other white cell types, which shift the share
- Method: automated analyzers read basophils less accurately than other white cells
- Steroid medicines, which can lower the count
- Allergic reactions, which can change it
- Whether your lab sets a range: Labcorp prints none, while ARUP lists 0.3 to 1.4 percent
- The percent is a share of all white cells, so it falls when other white cells rise (for example neutrophils during an infection) and rises when they fall, even if the number of basophils has not changed.
- 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.
- Steroid medicines (corticosteroids) lowered basophil counts in healthy volunteers.
When to talk to a clinician
The percent alone rarely needs urgent action. Talk with your clinician if the absolute basophil count is high again on a repeat test, or if a high basophil count 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
- Should I track the percent or the absolute count over time?
- What is my lab's range for basophils, and was anything flagged?
- Is my absolute basophil count also high?
- Could allergies or long-lasting inflammation explain this?
- Is a low or zero basophil percent expected with my lab's method?
Questions people ask
What is a typical basophil percentage?
Usually well under 2 percent of your white blood cells. ARUP lists 0.3 to 1.4 percent and other sources give similar ranges, such as about 0.5 to 1 or 0.6 to 1.8 percent. Some labs set no range for the percent.
Why does my report show no range for basophil percent?
Some labs, including Labcorp, do not set a range for white cell percents and print 'Not Estab.' (not established). The absolute basophil count on the same report is the more useful number.
Is a basophil percent of 0 a problem?
Usually not. Basophils are so rare that 0 percent is a common result in healthy people, and automated machines tend to under-read them.
How do I get the absolute count from the percent?
Multiply the percent by your total white blood cell count and divide by 100. For example, 1 percent of a white count of 6.0 ×10³/µL is 0.06 ×10³/µL.
Show the science and sources
Units
- 1 % = 1 %
- 1 % = 0.01 fraction (0–1)
Open the Basophils (%) unit converter
For clinicians and researchers
Reported as basophils per 100 leukocytes (LOINC 706-2 for automated counts and 707-0 for manual counts; LOINC also defines a number-fraction code, 71680-3). The CLSI reference method is a manual differential of 400 leukocytes on a stained smear. Automated analyzers produce the percent by flow cytometry, but basophil counts are the least accurate of the five-part differential and tend to underestimate. Absolute count equals percent times the total white cell count divided by 100, so 1 percent of a count of 6.0 ×10³/µL is 0.06 ×10³/µL. Because the percent is relative, a shift in neutrophils or lymphocytes changes it independently of the basophil number. Reference intervals for the percent are not harmonized: ARUP 0.3 to 1.4 percent, Labcorp not established, and textbook values of about 0.6 to 1.8 percent. StatPearls describes basophilia in absolute terms (above about 200 cells/µL). Unexplained persistent basophilia, especially with left-shifted neutrophilia or circulating blasts, prompts smear review and evaluation for a myeloproliferative neoplasm.
LOINC 706-2 (primary), 707-0, 30180-4, 71680-3. Specimen: whole-blood.
Sources
- CBC with Platelet Count and Automated Differential (test 0040003), hotline effective March 1, 2021: reference intervals, ARUP Laboratories (2021)
- Normal Values for Leukocyte Concentration in Blood (Table 63-1), Harrison's Principles of Internal Medicine, 19th edition (McGraw-Hill) (2015)
- Blood differential test, MedlinePlus Medical Encyclopedia (National Library of Medicine) (2025)
- Sample patient report, test 005013 (CBC with Diff, Platelet, NLR), Labcorp
- Basophilia, StatPearls (NCBI Bookshelf) (2024)
- 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-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.