A platelet aggregation test is one of several coagulation tests (types of blood tests) used to measure the time it takes for an individual’s blood to clot. The test is most often used to determine why a patient is showing abnormal bleeding despite having a normal platelet count, which is measured during a CBC blood test. Regular platelet aggregation tests may also be ordered for patients who take antiplatelet medications to monitor the effects of treatment. 

Platelets (thrombocytes) are small cells in the bloodstream that are produced in the bone marrow. When an individual bleeds, platelets clump together at the injury site, swell and become attached to the injured area. This process acts a plug to reduce further bleeding.

Patients who are scheduled for a platelet aggregation test will be advised not to eat or drink anything for eight to 12 hours before the test. Alternatively, they may be instructed to consume only non-fat foods and beverages to avoid any fats in the blood that could interfere with test results. Furthermore, changes may be necessary in the way patients take certain medications before the test.