The platelet aggregation test checks to see how well platelets, a part of blood, clump together and cause blood clotting.

A blood sample is needed. For information on how this is done, see: Venipuncture

The laboratory specialist will look at how the platelets spread out in the liquid part of the blood (plasma) and whether they form clumps after a certain chemical or drug is added. When platelets clump together, the blood sample is more clear. A machine measures the changes in cloudiness and prints a record of the results.

Many medications may affect test results. Tell your health care provider about any medications (including over-the-counter drugs) you have taken within 2 weeks before the test.

Medications that may affect test results include:

• Antibiotics: penicillins, cephalosporins, nitrofurantoin
• Antihistamines
• Aspirin
• Aspirin-containing compounds
• Clopidogrel
• Dipyridamole
• Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen and naproxen
• Theophylline
• Ticlopidine
• Tricyclic antidepressants

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Your doctor may order this test if you have signs of a bleeding disorder or low platelet count, or if a member of your family has a known bleeding disorder due to platelet dysfunction.

The test can help diagnose problems with platelet function and determine whether the problem is due to your genes, another disorder, or a side effect of medicine.

See also: Platelet count

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Platelet aggregation test Results

Review Date: 02/28/2011
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. 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)