Definition of Platelet aggregation test:

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

How the test is performed:

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.

How to prepare for the test:

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

How the test will feel:

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.

Why the test is performed:

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