Lab result explainedBlood count (CBC)Last updated November 11, 2026

Absolute basophils (baso abs): normal range, what 0.1 means and causes of a high basophil count

Absolute basophil count (Baso abs) · Complete blood count (CBC) with differential · reported in ×10³/µL (K/µL, thousand per microliter) or cells/µL; 0.1 ×10³/µL = 100 cells/µL = 0.1 ×10⁹/L

The absolute basophil count ("baso abs" or "basophils absolute" on a CBC with differential) is the number of basophils in a microliter of blood, calculated by multiplying the total white cell count by the basophil percentage. Basophils are the rarest white cell, making up less than 1 percent of the total, and they carry granules of histamine and heparin that they release during allergic reactions and in defense against parasites. In adults the normal range is about 0 to 0.1 ×10³/µL, which is 0 to 100 cells per microliter, or 0 to 1 percent of white cells. A result of 0.1 is therefore normal, and 0 is the most common result of all.

Because basophils are so scarce, small changes look large. A count of 0.2 ×10³/µL is only 100 cells above the upper limit yet is twice 'normal', and automated analyzers are least precise for this cell, so a single borderline result is often an artifact or a transient response to allergy, infection or a skipped thyroid tablet. A genuinely and persistently raised basophil count (basophilia) is uncommon and has a short list of causes: allergic and inflammatory conditions, hypothyroidism, iron deficiency, some infections, and the myeloproliferative neoplasms, above all chronic myeloid leukemia (CML), where basophilia is a hallmark and a marker of disease stage.

A low basophil count is not a meaningful finding, since zero is within the normal range; the causes of 'basopenia' (acute stress, steroids, hyperthyroidism, an acute allergic reaction) are covered briefly here for people who search for it. This page explains the ranges, when a high baso abs matters, what to read it with and what happens next.

Baso abs at a glance

What it is: the number of basophils per microliter of blood, the rarest white cell, carrying histamine and heparin granules involved in allergic responses.
Normal (adults): about 0–0.1 ×10³/µL (0–100 cells/µL), or 0–1 percent of white cells; some labs allow up to 0.2 or 2 percent. A result of 0.1 is normal and 0 is common. Labs differ.
High (basophilia): above 0.1–0.2 ×10³/µL depending on the lab. Common causes are allergy, chronic inflammation (ulcerative colitis, rheumatoid arthritis), hypothyroidism, iron deficiency and some infections; a persistent count above 0.2, or any count above 1.0, raises concern for chronic myeloid leukemia or another myeloproliferative neoplasm.
Low basophils (0) are normal and need no action; counts fall further with steroids, stress, hyperthyroidism and during an acute allergic reaction.
Automated counters are least accurate for basophils, so an unexpected result is usually confirmed by a smear review before anything else is done.
Next step: repeat when well; if persistently raised, check thyroid function, ferritin, CRP and a smear; if above 0.2 with high white cells, high platelets or an enlarged spleen, test for the BCR-ABL1 fusion and JAK2 mutation.

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What Baso abs measures

Basophils are granulocytes made in the bone marrow under the influence of interleukin-3; they circulate for a few days before entering tissue and are the blood-borne relatives of tissue mast cells. Their dark-staining granules contain histamine, heparin, leukotriene precursors and proteases, released when allergen cross-links IgE on the cell surface. They amplify allergic inflammation, help defend against ticks and worms, and in normal blood number only 20 to 100 per microliter, about one cell in every 100 to 200 white cells.

Automated analyzers identify basophils by their resistance to a lysing agent or by light scatter after a specific stain and report a percentage and an absolute count, the latter being the percentage multiplied by the total white cell count. Because the true number is so small, the statistical error is large: a count of 0.1 ×10³/µL differs from 0.2 by a handful of cells per hundred counted, and analyzers may misclassify lipemic samples, nucleated red cells or abnormal lymphocytes as basophils. For this reason a raised basophil count is confirmed on a manual 100- or 200-cell differential before it is acted on, and even manual counts have wide confidence intervals at these percentages.

Units of 0.1 ×10³/µL, 0.1 K/µL, 0.1 ×10⁹/L and 100 cells/µL all mean the same thing. The count has a mild daily rhythm, is slightly lower at ovulation and in pregnancy, rises modestly in winter and in some people after a meal, and falls within hours of corticosteroids, adrenaline or an acute allergic reaction as basophils leave the blood for tissue. None of these shifts normally moves the count outside the reference range.

Normal range for Baso abs

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (×10³/µL (K/µL, thousand per microliter) or cells/µL; 0.1 ×10³/µL = 100 cells/µL = 0.1 ×10⁹/L)	Notes
Adults, normal	0–0.1 ×10³/µL (0–100 cells/µL); 0–1 percent of white cells	Some labs print 0.0–0.2 or allow up to 2 percent. A result of 0 or 0.1 is normal. Labs differ; use the printed range.
Children	About 0–0.2 ×10³/µL	Similar percentages to adults; higher total white counts in young children give slightly higher absolute numbers.
Borderline	0.1–0.2 ×10³/µL (100–200 cells/µL)	Flagged by some labs and not others. Usually analyzer imprecision, allergy or recent infection; repeat when well before investigating.
Mild basophilia	0.2–0.5 ×10³/µL (200–500 cells/µL)	Allergy, chronic urticaria in remission, hypothyroidism, iron deficiency, inflammatory bowel disease, recovery from infection, early myeloproliferative neoplasm.
Marked basophilia	Above 0.5–1.0 ×10³/µL (over 500–1,000 cells/µL)	Uncommon outside myeloproliferative neoplasms; chronic myeloid leukemia is the leading cause, especially with a high white count, high platelets and an enlarged spleen.
Chronic myeloid leukemia, accelerated phase	Basophils 20 percent or more of white cells	One of the WHO and International Consensus criteria for progression from chronic phase; a rising basophil percentage during chronic phase is an adverse sign.
Low (basopenia)	0 ×10³/µL	Within the normal range; not a diagnosis. Lower still in relative terms with corticosteroids, stress, hyperthyroidism and acute allergic reactions.

High absolute basophils (basophilia)

A high baso abs means your basophil count is above the lab's upper limit, usually 0.1 or 0.2 ×10³/µL. The first question is whether it is real: basophils are the cell automated counters get wrong most often, so a borderline result with every other count normal is commonly a counting artifact or a brief reactive change, and is repeated and checked on a smear. When the rise is confirmed and modest (0.2 to 0.5), the usual explanations are allergic conditions such as allergic rhinitis, asthma, food or drug allergy and chronic urticaria; chronic inflammatory diseases, particularly ulcerative colitis, Crohn's disease and rheumatoid arthritis; hypothyroidism, in which thyroid hormone deficiency slows basophil clearance; iron deficiency; and the recovery phase of infections such as chickenpox, influenza, tuberculosis and some helminth infections.

The reason clinicians take basophilia seriously is its association with the myeloproliferative neoplasms, a group of chronic bone marrow cancers that overproduce mature blood cells. In chronic myeloid leukemia (CML), basophils are raised in almost every patient at diagnosis, typically alongside a white cell count of 50 to 200 ×10³/µL, immature granulocytes on the smear, high platelets and an enlarged spleen, and the basophil percentage is a staging marker: 20 percent or more defines the accelerated phase. Polycythemia vera, essential thrombocythemia, primary myelofibrosis and systemic mastocytosis also raise basophils, usually with a high hematocrit, high platelets or raised tryptase respectively.

A persistent absolute basophil count above 0.2 ×10³/µL with no allergic, thyroid, iron or inflammatory explanation, or any count above 1.0, therefore prompts a smear review, a BCR-ABL1 test for CML and a JAK2 mutation test, together with a check of the other cell lines and the spleen. Basophilia alone, with normal white cells, hemoglobin and platelets and no symptoms, is very rarely a blood cancer.

Common causes

Allergic disease and hypersensitivity
Allergic rhinitis, asthma, atopic dermatitis, food and drug allergy and chronic urticaria can raise basophils to 0.2 to 0.4 ×10³/µL, often with eosinophils raised too. During an acute reaction the count may briefly fall as basophils enter tissue, then rise in the days after.
Chronic myeloid leukemia
Basophilia is present in nearly all patients at diagnosis and is one of the most specific clues, usually with a white count above 25 to 50 ×10³/µL, a full spectrum of immature granulocytes on the smear, raised platelets and splenomegaly. Confirmed by detecting the BCR-ABL1 fusion (Philadelphia chromosome). Basophils of 20 percent or more mark the accelerated phase.
Other myeloproliferative neoplasms
Polycythemia vera (high hematocrit, JAK2 V617F), essential thrombocythemia (platelets above 450 ×10³/µL), primary myelofibrosis (teardrop red cells, large spleen) and systemic mastocytosis (raised serum tryptase) each raise basophils modestly.
Hypothyroidism
Low thyroid hormone is associated with a mild rise in basophils that reverses with levothyroxine; a raised TSH on the same panel is the usual explanation in an otherwise well person.
Inflammatory bowel disease and other chronic inflammation
Ulcerative colitis in particular, Crohn's disease, rheumatoid arthritis and other chronic inflammatory states cause mild basophilia that tracks disease activity.
Iron deficiency
Iron deficiency anemia is a recognized cause of mild basophilia; the count falls as ferritin is restored.
Infections
Varicella (chickenpox), influenza, tuberculosis, smallpox historically, and helminth infections such as hookworm raise basophils, usually during recovery and alongside other white cell changes.
After splenectomy and in hemolytic anemia
Loss of the spleen's filtering raises counts of several cell types including basophils; chronic hemolysis and recovery from marrow suppression do the same.
Medications and estrogen
Estrogen therapy and some antithyroid drugs are associated with slight rises; the effect is small and rarely moves the count out of range.
Analyzer artifact
Lipemic (fatty) samples, nucleated red cells, abnormal lymphocytes and clumped platelets can be misread as basophils by automated counters; a smear review resolves this, which is why it is the first step.

Symptoms that can go with it

Usually none; most mild rises are found incidentally
Itching, hives, flushing, sneezing or wheeze with allergic causes
Tiredness, feeling cold, weight gain, constipation and dry skin with hypothyroidism
Fatigue, breathlessness on exertion and pale skin with iron deficiency
Abdominal pain, diarrhea or blood in the stool with inflammatory bowel disease
Fullness or discomfort under the left ribs, night sweats, weight loss, bone pain or easy bruising, which with a high white count suggest a myeloproliferative neoplasm
Itching after a warm shower, headaches and a red complexion in polycythemia vera

Low absolute basophils (basopenia)

A basophil count of 0 is a normal result and the most common one on healthy people's reports, so 'low basophils' is not a diagnosis. Analyzers simply cannot distinguish 0 from 20 cells per microliter with any reliability. When basophils are measured by more sensitive research methods, counts do fall below the usual baseline in a handful of situations: corticosteroid treatment and the cortisol surge of acute stress, infection or surgery; hyperthyroidism, where thyroid hormone speeds basophil clearance; ovulation and pregnancy; and during an acute allergic reaction or anaphylaxis, when basophils leave the blood for the tissues. Active chronic urticaria is also associated with low circulating basophils, which recover as the condition settles.

None of these requires any action directed at the basophils themselves. If your count is 0 and the rest of your CBC is normal, nothing further is needed. If you are investigating fatigue, weight loss, palpitations or heat intolerance, a TSH is a reasonable test, but the basophil count would not be the reason to order it.

Common causes

Normal variation
Zero is within the reference range; the true count in most healthy adults is 20 to 60 cells per microliter, below the resolution of routine counting.
Corticosteroids and acute stress
Prednisone, dexamethasone and the body's own cortisol during infection, surgery or trauma reduce circulating basophils and eosinophils within hours.
Hyperthyroidism
Excess thyroid hormone shortens basophil survival in the blood; the count recovers with treatment. Graves' disease and toxic nodules are the usual causes.
Acute allergic reaction or anaphylaxis
Basophils are recruited into tissue during an acute reaction, so a sample drawn at that time shows a transient fall.
Chronic spontaneous urticaria
People with active hives often have low blood basophils, thought to reflect migration into the skin; counts rise as the urticaria remits.
Ovulation and pregnancy
Hormonal shifts lower basophil counts slightly around ovulation and through pregnancy.

Symptoms that can go with it

None from the low count itself
Palpitations, heat intolerance, weight loss, tremor and anxiety if hyperthyroidism is present
Itchy welts in chronic urticaria, or the symptoms of the acute illness or allergic reaction that lowered the count

Read it alongside

Total white cell count — the absolute basophil count is the percentage multiplied by this; basophilia with a white count above 25 to 50 ×10³/µL is the setting in which CML is suspected.
Basophil percentage — a percentage of 10 to 19 is a warning sign and 20 or more defines accelerated-phase CML; in reactive basophilia the percentage rarely exceeds 3 to 5.
Absolute eosinophils — eosinophils and basophils rising together suggest allergy or a myeloproliferative neoplasm; eosinophils alone point more toward allergy, drugs or parasites.
Platelets and hematocrit — high platelets (essential thrombocythemia, CML) or a high hematocrit (polycythemia vera) alongside basophilia point to a myeloproliferative neoplasm.
Immature granulocytes, myelocytes and blasts — their presence on the smear with basophilia is the typical picture of CML and triggers BCR-ABL1 testing.
TSH and free T4 — hypothyroidism raises basophils and hyperthyroidism lowers them; a thyroid panel explains many otherwise puzzling results.
Ferritin — iron deficiency is a simple, correctable cause of mild basophilia.
Serum tryptase and IgE — tryptase is raised in systemic mastocytosis; total IgE supports an allergic cause.

What usually happens next

A single result of 0.1 ×10³/µL needs nothing; a first result of 0.2 or above with normal other counts is repeated in 4 to 8 weeks when you are well, with a request for a manual differential to confirm the cells are basophils.
If a mild rise is confirmed, expect a review of allergy symptoms and medications, a TSH, a ferritin, CRP and a look at the eosinophil count; treating hypothyroidism, iron deficiency or active inflammation usually normalizes the count.
Basophilia with a high white count, high platelets, a high hematocrit, immature cells on the smear or an enlarged spleen is referred to hematology for BCR-ABL1 (CML) and JAK2 V617F testing, and often a bone marrow examination.
A persistent, unexplained count above 0.2 ×10³/µL even with normal other counts deserves a smear review and a BCR-ABL1 test, because early CML can present with basophilia before the white count climbs.
Ask whether your previous CBCs show the same level; a basophil count that has sat at 0.1 to 0.2 for years is far less concerning than one that has risen.

Diet, lifestyle and natural levers with evidence

What can move Baso abs once the cause is known. Nothing here replaces finding the cause.

Control the allergic trigger

Moderate evidence

Reactive basophilia from allergic rhinitis, asthma or eczema falls as exposure and symptoms are controlled: avoiding a confirmed food or drug allergen, reducing dust mite and pet exposure where sensitization is proven, and standard treatment of the allergic disease all bring the count back into range over weeks. No herb or supplement has been shown in human trials to lower a basophil count; quercetin and vitamin C stabilize basophils and mast cells in laboratory studies, but trial evidence in people is limited to modest symptom relief in allergic rhinitis, not a change in the count.

Correct hypothyroidism and iron deficiency

Preliminary evidence

Both are common, reversible causes of a mildly raised basophil count. Levothyroxine replacement that brings TSH into range, and iron repletion that restores ferritin above about 30 to 50 ng/mL, are followed by normalization of the basophil count over two to three months in case series and clinical experience, although neither effect has been measured in randomized trials because the count itself is not a treatment target. The dietary levers are those for iron deficiency: red meat, legumes, fortified grains and vitamin C with plant iron, with iodine and selenium adequacy for thyroid health.

Do not start iron or thyroid supplements for a basophil result alone; both require a confirmed deficiency on blood tests.

Timing: steroids, acute illness and allergic reactions move the count

Strong evidence

Corticosteroids and the body's own cortisol during an acute illness pull basophils out of the blood within hours, and an acute allergic flare does the same, so a count taken then can mask a real basophilia; conversely, the recovery week after chickenpox, influenza or another infection can show a brief rise. For a repeat test intended to confirm or exclude basophilia, wait until you are well, at least a week off oral steroids if your clinician agrees, and ask for a manual differential. Nothing 'natural' changes the basophil count in a myeloproliferative neoplasm; those are treated by a hematologist.

When to see a clinician promptly

An absolute basophil count above 0.5 ×10³/µL, or any basophilia together with a white cell count above 25 ×10³/µL, platelets above 450 ×10³/µL or a hematocrit above 49 percent (men) or 48 percent (women): possible myeloproliferative neoplasm, needs prompt hematology assessment.
Basophilia with fullness or pain under the left ribs, night sweats, unexplained weight loss, bone pain or easy bruising and bleeding.
A basophil count above 0.2 ×10³/µL confirmed on two tests with no allergic, thyroid, iron or inflammatory explanation.
Basophilia with immature granulocytes, myelocytes or blasts reported on the smear, at any level.
Basophilia in someone with inflammatory bowel disease, iron deficiency or thyroid disease that fails to normalize once the underlying condition is treated.
Any white cell abnormality with high fever, confusion, severe headache, breathlessness or a fast heart rate, which needs same-day care regardless of the basophil count.

Frequently asked questions

What is a normal absolute basophil count?

About 0 to 0.1 ×10³/µL (0 to 100 cells per microliter), or 0 to 1 percent of white cells, on most US reports; some labs allow up to 0.2 or 2 percent. Zero is the most common result and is entirely normal. Compare with the range printed on your own report because laboratories differ and automated counters are least precise for this cell.

Is basophils 0.1 high?

No. A count of 0.1 ×10³/µL (100 cells/µL) is at the upper edge of the normal range on most reports and well within range on others. It needs no action and no repeat. If the percentage is also 1 or 2 percent and every other count is normal, this is an unremarkable result.

What does baso abs high mean on a blood test?

It means your absolute basophil count is above your lab's upper limit, usually 0.1 or 0.2 ×10³/µL. Because basophils are so rare and analyzers miscount them easily, a borderline result is often repeated and checked on a smear first. Confirmed mild rises usually come from allergies, chronic inflammation, an underactive thyroid, iron deficiency or recovery from an infection; a count above 0.2 that persists, or any high count alongside a high white count, high platelets or an enlarged spleen, is tested for chronic myeloid leukemia and other myeloproliferative neoplasms.

Is basophils 0.2 or 0.3 something to worry about?

A count of 0.2 ×10³/µL is borderline and 0.3 is mild basophilia. With a normal white count, hemoglobin and platelets and no symptoms, both are most often reactive (allergy, thyroid, iron, inflammation) or an artifact, and the usual step is a repeat with a manual differential in a month or two. They become more significant if they persist, rise over time, or are accompanied by other abnormal counts, in which case a BCR-ABL1 test for CML is reasonable.

Can high basophils mean leukemia?

Sometimes. Basophilia is a hallmark of chronic myeloid leukemia, where it almost always comes with a white cell count of 50 to 200 ×10³/µL, immature granulocytes on the smear, high platelets and an enlarged spleen; the diagnosis is confirmed by the BCR-ABL1 fusion gene. Basophils of 20 percent or more of white cells mark the accelerated phase. Isolated mild basophilia with otherwise normal counts is very rarely leukemia, but a persistent unexplained count above 0.2 ×10³/µL does warrant a BCR-ABL1 test because early CML can present this way.

Can allergies raise basophils?

Yes. Allergic rhinitis, asthma, eczema, food and drug allergy and chronic urticaria can all raise the basophil count to 0.2 to 0.4 ×10³/µL, usually with eosinophils raised too. Interestingly, during an acute allergic reaction the blood count may briefly fall as basophils move into tissue, then rise in the following days. Controlling the allergic disease brings the count back into range.

What does low basophils or basophils 0 mean?

Nothing by itself. Zero is within the normal range and is the single most common result, because the true count in most people is below what routine analyzers can resolve. Counts do fall with corticosteroids, acute stress or infection, hyperthyroidism, ovulation, pregnancy and acute allergic reactions, but none of these needs treatment directed at the basophils. If the rest of your CBC is normal, no follow-up is needed.

References

Blood differential test. MedlinePlus, US National Library of Medicine (2023)View source
Basophilic disorders. Merck Manual Professional Version (2024)
Chronic myeloid leukemia (CML). Merck Manual Professional Version (2024)
Riley LK, Rupert J. Evaluation of patients with leukocytosis. American Family Physician (2015)
Valent P, Sotlar K, Blatt K, et al.. Proposed diagnostic criteria and classification of basophilic leukemias and related disorders. Leukemia (2017)
Siracusa MC, Kim BS, Spergel JM, Artis D. Basophils and allergic inflammation. Journal of Allergy and Clinical Immunology (2013)
Arber DA, Orazi A, Hasserjian RP, et al.. International Consensus Classification of Myeloid Neoplasms and Acute Leukemias: integrating morphologic, clinical, and genomic data. Blood (2022)
Hochhaus A, Baccarani M, Silver RT, et al.. European LeukemiaNet 2020 recommendations for treating chronic myeloid leukemia. Leukemia (2020)
Buttarello M, Plebani M. Automated blood cell counts: state of the art. American Journal of Clinical Pathology (2008)
Mitre E, Nutman TB. Basophils, basophilia and helminth infections. Chemical Immunology and Allergy (2006)
Chronic myelogenous leukemia. Mayo Clinic (2024)View source

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.