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Alternative names
Eosinophils; Absolute eosinophil countDefinition Return to top
This is a test to measure the number of eosinophils (a type of white blood cell) in the blood. (See also blood differential.)How the test is performed Return to top
Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.
For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.
In the laboratory, the blood is placed on a microscope slide and a stain is added that causes eosinophils to show orange-red granules. The technician then counts how many eosinophils there are per 100 cells. The percentage of eosinophils is multiplied by the white blood cell count to give the absolute eosinophil count.
How to prepare for the test Return to top
No special preparation is necessary.How the test will feel Return to top
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.Why the test is performed Return to top
Eosinophils are white blood cells active in allergic diseases, parasitic infections, and other disorders. An eosinophil count may be ordered if the blood differential is abnormal, or if there is suspicion of specific diseases.Normal Values Return to top
Less than 350 cells/mcl (cells per microliter)What abnormal results mean Return to top
Increased eosinophils (eosinophilia) is most often associated with allergic diseases and parasites (such as worms).What the risks are Return to top
Special considerations Return to top
The eosinophil count is nonspecific (it does not tell, for example, if an increase is caused by allergy or parasite infection). It is most often used to confirm a diagnosis.
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Page last updated: 28 October 2004 |