A test for platelet-associated antibodies shows whether you have antibodies that are directed against platelets in your blood.

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The area 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. 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 special preparation is necessary for adults.

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.

This test may be ordered when you have a low platelet count (thrombocytopenia). It is used to detect antibodies against platelets.

A negative test is normal.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

Abnormal results show that you have antiplatelet antibodies. These are proteins made by the body that attach to platelets and destroy them. This causes a low platelet count, which can lead to excessive bleeding.

Antiplatelet antibodies may appear in the blood for unknown reasons (idiopathic thrombocytopenic purpura), or as a side effect of certain drugs such as heparin. These drugs can sometimes cause the immune system to identify its own platelets as abnormal or foreign, and attack them.

Veins and arteries vary in size from one patient to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Current tests cannot tell for sure whether a low platelet count (thrombocytopenia) is caused by immune problems. Therefore, your doctor will make a diagnosis based on other tests and examinations.

This test is often performed because you have a bleeding problem. Bleeding may be more of a risk for you than for people who do not have bleeding problems.

McMillan R. Hemorrhagic disorders: Abnormalities of platelet and vascular function. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 179.