Most of the time blood is drawn from a vein on the inside of the elbow or the back of the hand. The site is cleaned with an antiseptic. The health care provider wraps an elastic band around your upper arm to make the vein swell with blood.

Next, the provider gently inserts a needle into the vein. The blood collects into an airtight tube attached to the needle. The elastic band is removed from your arm. The needle is then removed and the site is covered to stop bleeding.

In infants or young children, a sharp tool called a lancet may be used to prick the skin. The blood collects in a small glass tube, or onto a slide or test strip. A bandage is put on the spot to stop bleeding.

In the lab, the blood is placed on a microscope slide. A stain is added to the sample. This causes eosinophils to show up as orange-red granules. The technician then counts how many eosinophils are present per 100 cells. The percentage of eosinophils is multiplied by the white blood cell count to give the absolute eosinophil count.

The reference range for adults (males and females) is as follows:

Total leukocytes: 4.00-11.0 x 10 9/L

Neutrophils: 2.5–7.5 x 10 9/L

Lymphocytes: 1.5–3.5 x 10 9/L

Monocytes: 0.2–0.8 x 10 9/L

Eosinophils: 0.04-0.4 x 10 9/L

Basophils: 0.01-0.1 x 10 9/L