An eosinophil count is a blood test that measures the number of eosinophils, a type of white blood cell, in the body. Eosinophils are part of the immune system and become active when the body is fighting certain allergic diseases, infections, and other medical conditions. The test is typically ordered as part of a complete blood count (CBC) to get a good picture of overall health.

The test is performed by drawing blood from a vein on the inside of the elbow or the back of the hand. The site is cleaned with an antiseptic, and an elastic band is wrapped around the upper arm to make the vein swell with blood. A technician will add a special stain to the blood sample to make the eosinophils visible and count how many are present in every 100 cells. They will then multiply that percentage by the white blood cell count to get the absolute eosinophil count.

A high eosinophil count may indicate that the immune system is fighting an infection from a virus, bacteria, or fungus, or experiencing an allergic reaction. It may also be a sign of another health condition, such as an autoimmune disease. A low eosinophil count may be due to alcohol intoxication or overproduction of certain steroids in the body.

Overall, an eosinophil count is a useful tool for doctors to determine the number of eosinophils in the bloodstream and to help diagnose certain conditions.