Platelet count

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A platelet count is a test to measure how many platelets you have in your blood. Platelets help the blood clot. They are smaller than red or white blood cells.

Thrombocyte count

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

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Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

No preparation is necessary. Tell your doctor if you are taking any medications, including over-the-counter medicines and supplements.

Drugs that can lower platelet counts include chemotherapy drugs, chloramphenicol, colchicine, GP IIb/IIIa receptor antagonists, H2 blocking agents, heparin, hydralazine, indomethacin, isoniazid, quinidine, streptomycin, sulfonamides, thiazide diuretic, and tolbutamide.

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.

The number of platelets in your blood can be affected by many diseases. Platelets may be counted to monitor or diagnose diseases, or identify the cause of excess bleeding.

Review Date: 02/13/2011
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org).