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Complete Blood Count
Review status
Currently under review
Pending specialist review and validation.
This test reports the proportion of basophils among your white blood cells. Basophils are a small group of immune cells that store histamine and other mediators involved in allergic responses and inflammation. The result is shown as a percentage of all white blood cells counted on a complete blood count with differential.
Modern analyzers measure this percentage from a tube of your blood and can be confirmed by a trained professional reviewing a blood smear when needed. The relative value reflects how basophils compare to the other white blood cell types, not the total number in your bloodstream.
Basophil percentage helps your clinician understand allergic conditions, chronic inflammation, and certain infections. It can also provide clues to bone marrow disorders that change how white blood cells are produced. The test is usually ordered as part of a complete blood count with differential when evaluating symptoms like persistent itching, hives, nasal allergies, asthma flares, or unexplained inflammation, and when monitoring known hematologic conditions.
Changes in the basophil percentage can occur because basophils themselves change or because other white blood cell types increase or decrease. Looking at this percentage alongside symptoms, examination, and other lab results helps determine whether the finding is a normal variation, related to allergy or infection, or suggests a marrow process that may need further assessment.
Most people have a very small proportion of basophils, and minor day‑to‑day shifts are common. A single mildly higher or lower result often reflects transient factors such as recent illness, stress, or medication effects and usually is not urgent by itself.
If your result is persistently higher and you have symptoms of allergy or inflammation, your clinician may consider allergic disease, thyroid conditions, chronic infections, or less commonly a bone marrow disorder. A very low percentage is typically not concerning on its own. Your care team may review trends over time, compare with the absolute basophil count, and consider further tests such as a repeat complete blood count, peripheral smear review, or targeted evaluations based on your history. Discuss any questions with your clinician so results are interpreted in the context of your overall health.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Allergic rhinitis, eczema, urticaria, or recent exposure to allergens can raise basophil activity and may be associated with a higher relative percentage.
Some parasitic and chronic inflammatory infections can increase basophils and other white blood cells, shifting the relative percentage upward.
Corticosteroids and some immunosuppressants can lower basophils, while certain cancer therapies or biologics can alter white blood cell distributions.
Thyroid disorders and other systemic conditions can affect white blood cell production and proportions, changing the basophil percentage.
During acute infections or physiologic stress, increases in other white blood cells can dilute the proportion of basophils and lower the relative value.
Delayed processing, inadequate mixing, or instrument flags may affect the reported differential. Proper collection and timely analysis help ensure accuracy.
Physiologic changes in pregnancy and in early life can mildly shift white blood cell differentials. Results are interpreted alongside clinical context.
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