Basophils (absolute and %) are the least common white blood cells, typically comprising ~0.5–1% of leukocytes, with an absolute range of ~0.01–0.09 × 10⁹/L. They play a role in allergic responses and immune signaling, releasing histamine and inflammatory mediators.

In healthy individuals, basophil levels are usually very low and somewhat variable. Mild fluctuations are rarely meaningful. Higher levels may be seen with allergic conditions, chronic inflammation, or, less commonly, bone marrow disorders. Given measurement limitations and their low baseline numbers, basophils are best interpreted only when clearly elevated and in clinical context.