Basophils account for less than 3% of the circulating white blood cells (0 to 300 basophils per microliter of blood). These cells have some role in immune surveillance and wound repair. Basophils can release histamine and other mediators and play a role in the initiation of allergic reactions. A decrease in the number of basophils (basopenia) can occur as a response to thyrotoxicosis, acute hypersensitivity reactions, and infections. An increase in the number of basophils (basophilia) can occur in people with hypothyroidism. In the myeloproliferative disorders (for example, polycythemia vera and myelofibrosis), a marked increase in the number of basophils can occur.

Last full review/revision January 2013 by Mary Territo, MD