Basophils in a blood test: normal range and results (BAS)
The share of all white blood cells (in the white cell differential); laboratories also give the absolute number in ×10⁹/l, and intervals can differ slightly depending on the laboratory
- Updated
- 2026-09-10
- Every number with its source
What basophils are
Basophils are one of the five types of white blood cell (leukocyte), made in the bone marrow together with neutrophils, lymphocytes, monocytes and eosinophils. There are fewer of them in the blood than of any other type of white blood cell — usually less than 1 % of the whole white blood cell count. Basophils store histamine and other substances that they release during an allergic or inflammatory reaction, which is why they are linked to allergies, urticaria (hives), asthma and parasitic infections. The amount of basophils is determined by a white cell differential (a blood differential test) — the part of a full blood count that shows the percentage and the absolute number of each type of white blood cell. Because there are naturally very few basophils, even small fluctuations can look significant when expressed as a percentage, so a doctor assesses them together with the other values of the white cell differential and the whole clinical picture, rather than on their own.
The reference range for basophils
| Group | Range, % | Source |
|---|---|---|
| Adults The share of all white blood cells (in the white cell differential); laboratories also give the absolute number in ×10⁹/l, and intervals can differ slightly depending on the laboratory | 0.5–1 | MedlinePlus Reviewed 2025-02-03 |
When basophils are tested
- As part of a full blood count with a white cell differential — for prevention, before operations, while ill
- When an allergic reaction or chronic inflammation is suspected
- When the total white blood cell count has changed and it needs to be established which type of white cell has changed
- When monitoring treatment that affects the bone marrow, or diseases of the blood
- When rare diseases of the blood are suspected — for example chronic myeloid leukaemia
How to prepare
- Special preparation is usually not needed
- It is worth telling your doctor about recent infections or allergic reactions, because they can temporarily change the result
Raised basophils (basophilia)
Raised basophils (basophilia) can be linked to allergic reactions, chronic inflammation or autoimmune connective tissue diseases. Other possible causes are bone marrow (myeloproliferative) diseases, among them chronic myeloid leukaemia, and also chickenpox or the state after removal of the spleen. Which other type of white cell has changed alongside helps to establish the cause.
- An allergic reaction
- Connective tissue (collagen vascular) diseases
- Myeloproliferative diseases — a group of bone marrow diseases
- Chronic myeloid leukaemia — a type of bone marrow cancer
- Chickenpox
- The state after removal of the spleen
What is usually assessed alongside a raised result:
- The complete white cell differential — which other type has changed
- Signs and symptoms of allergy or chronic inflammation
- Family and illness history with regard to bone marrow diseases
- A repeat test to clarify the cause
Reduced basophils
Reduced basophils can be linked to an acute infection, a severe injury or cancer. Because there are anyway fewer basophils in the blood than of any other type of white cell, a small reduction often has no clinical significance and is assessed together with the other values of the white cell differential.
- An acute infection
- Cancer
- A severe injury
What is usually assessed alongside a reduced result:
- The total white blood cell count and the complete white cell differential
- A recent infection or injury
- A repeat test after recovery
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Frequently asked questions
›What is the normal basophil count in blood?
According to the MedlinePlus medical encyclopedia, in adults basophils make up 0.5–1 % of all white blood cells. Laboratories also give the absolute number (×10⁹/l), and the exact interval can differ slightly depending on the laboratory.
›Why are basophils considered the rarest type of white blood cell?
Of all five types of white blood cell — neutrophils, lymphocytes, monocytes, eosinophils and basophils — there are naturally fewest basophils in the blood, most often less than 1 % of the whole white blood cell count.
›What do raised basophils mean?
Raised basophils can be linked to an allergic reaction, chronic inflammation or a connective tissue disease. Another possible cause can be a bone marrow disease, among them chronic myeloid leukaemia — this is discussed with a doctor together with the complete white cell differential.
›What do reduced basophils mean?
Reduced basophils can be linked to an acute infection, a severe injury or cancer. Because there are naturally few of them, a small reduction often has no separate clinical significance without other changes.
›How is a basophil test done?
Basophils are determined in the white cell differential (a blood differential test) — a part of a full blood count, for which a blood sample is taken from a vein. Special preparation is usually not needed.
›Do you need to avoid eating before a basophil test?
No, MedlinePlus states that no special preparation is needed. It is worth mentioning to your doctor recent infections or allergic reactions, because they can temporarily change the result.
Sources
Related markers
This site is not an emergency service. If severe chest or head pain, breathlessness, confusion, difficulty speaking, heavy bleeding or another acute problem has come on suddenly — do not wait for tests, call 112.
This information is not a diagnosis and does not replace a consultation with a doctor. Reference ranges depend on the laboratory, your age and sex — always compare your result with the range printed on your own report.