Basophils (Absolute)

Basophils carry chemicals such as histamine inside small granules. When the cells are activated, they release these chemicals, which causes the swelling, itching, and breathing changes that you can feel during an allergic reaction or asthma attack.

Basophils make up only about 1% of your white blood cells, so the absolute basophil count is normally a very small number. Even small changes can sometimes give a clue to what is happening with your immune system or your bone marrow.

A higher than normal absolute basophil count (basophilia) may be linked to allergies, asthma, parasitic infections, an underactive thyroid (hypothyroidism), long-lasting inflammation, or certain bone marrow disorders such as chronic myeloid leukemia.

A lower than normal absolute basophil count (basopenia) is hard to detect because basophils are normally so few. It can be seen with severe allergic reactions, infections, an overactive thyroid (hyperthyroidism), pregnancy, or after taking steroid medicines.

Because basophils are normally a very small share of white blood cells, small changes in the count are usually viewed alongside the rest of your CBC and your symptoms. If your result is unusual, your provider may repeat the test or order other tests to find the cause.