Platelet Aggregation Test. A platelet aggregationtest checks how well your platelets clump together.Platelets are types of blood cells. They help form blood clots by sticking together. A clot is what stops the bleeding when you have a wound. Platelet aggregation is part of the sequence of events leading to the formation of a thrombus (clot). Aspirin, the most commonly used antiplatelet drug changes the balance between prostacyclin (which inhibits platelet aggregation) and thromboxane (that promotes aggregation).