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Basophils
The rarest white blood cells — participants of allergic reactions. Marked growth is uncommon and needs a hematologist's review.
Other names: Basophils, BAS, BASOSection: Blood cells
Updated: August 31, 2026·MedProtect editorial team Reference information — not a diagnosis or a prescription
In shortBasophils are the rarest leukocytes — allergy-response cells carrying histamine and heparin. A typical share is 0.5–1% of all leukocytes; zero values are a normal variant. Persistent growth is uncommon and needs a hematologist.
Reference ranges
Group
Reference range
Share of all leukocytes
0.5–1%
The source gives 0.5–1% of all white blood cells; because the cell count is so small, some labs set the reference from 0%. 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
Basophils are the smallest leukocyte population. Their granules hold histamine and heparin: on contact with an allergen the cells release these substances, triggering an immediate-type reaction — swelling, itching, bronchospasm.
Because basophils are normally so few, even a small absolute shift visibly changes their percentage. Persistent basophilia is a rare finding: it occurs in chronic inflammation, allergies, hypothyroidism and myeloproliferative disease, so it deserves an in-person review.
When it is high
Allergic reactionsFood and drug allergy, atopy flares can raise basophils.
Chronic inflammationUlcerative colitis, rheumatoid arthritis and other lingering inflammation.
HypothyroidismReduced thyroid function sometimes comes with basophilia.
Blood disordersChronic myeloid leukemia and other myeloproliferative diseases — the main cause of marked basophilia.
When it is low
Normal variantZero or near-zero basophils are a common finding in healthy people and not a problem by itself.
Acute allergic reactionAt the height of a reaction, basophils release their granules and temporarily 'disappear' from the count.
Steroids, stress, pregnancyPhysiological and drug-related lowering without clinical significance.
What can skew the result
These factors can shift the value without any disease — worth considering before a retest:
Allergic reactionsGlucocorticoidsCounting error at very low cell numbers
How to prepare
Taken within a morning fasting CBC with differential. No special preparation. Because the share of cells is tiny, automated counters sometimes err — a doubtful result is retested, with a manual differential if needed.
When a retest makes sense
For a slight excess — retest in 2–4 weeks; persistent growth means a planned visit to a GP or hematologist.
Who usually reviews this result
A result outside the reference range is usually reviewed by: GP or pediatrician; persistent basophilia — 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: BasophilsBASBASO
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.
No. Basophils are scarce in blood to begin with, and a zero reading is normal for healthy people. Low basophils have practically no clinical meaning.
Basophils 2% — what does it mean?
A slight excess is most often linked to allergy or inflammation. Retest in 2–4 weeks: persistent growth is a reason to see a GP and, if needed, a hematologist.
Are basophils directly tied to allergy?
Yes — these are the cells of the allergic reaction, releasing histamine on contact with an allergen. But allergy is diagnosed from symptoms and specific tests, not from basophils alone.
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