basophilia

Basophilia is the elevation of basophils in the peripheral blood. It is typically defined by an absolute basophil count greater than about 0.2 x 10^9/L or a basophil fraction above roughly 2% of circulating white blood cells. Basophils are granulocytes that participate in allergic responses and defense against parasites, releasing mediators such as histamine and heparin.

Basophilia is relatively uncommon and usually signals an underlying condition. Reactive (secondary) basophilia can accompany allergic diseases, viral or bacterial infections, autoimmune disorders, thyroid disease, pregnancy, stress, or post-splenectomy. Certain drugs can also induce basophilia. Primary basophilia is often seen in myeloproliferative neoplasms, particularly chronic myeloid leukemia (CML) and other disorders with clonal myeloid proliferation.

Diagnosis relies on a complete blood count with differential, review of the patient’s history and exam, and targeted testing when persistent basophilia or accompanying hematologic abnormalities are present. If reactive causes are excluded or clonal disease is suspected, testing may include mutations commonly associated with myeloproliferative neoplasms (JAK2, CALR, MPL) and consideration of bone marrow examination to assess cellularity and lineage involvement.

Management aims at the underlying condition. Reactive basophilia typically decreases with successful treatment of the trigger. In myeloproliferative neoplasms, disease-directed therapy (for example, tyrosine kinase inhibitors in CML) can reduce basophilia as part of overall response. Prognosis depends on the underlying diagnosis, with basophilia in CML often reflecting higher disease activity and prognosis.

Basophils and basophilia. See also basophil.