Platelet Aggregation Test

What do Abnormal Results Mean?

Congenital disorders that cause decreased platelet aggregation:

• Glanzmann's thrombasthenia (a rare inherited platelet disorder) -- platelets fail to aggregate in response to normal stimulation but do clump normally in response to ristocetin.
• Bernard-Soulier syndrome (a rare inherited disorder in which platelets are unable to respond to von Willebrand factor) -- platelets aggregate normally in response to most stimulation but do not aggregate in response to ristocetin. The response to collagen is blunted.
• Storage pool disease (a group of disorders characterized by defective stimulation by materials, especially ADP, which trigger platelet aggregation)-- variable abnormalities of platelet aggregation
• Von Willebrand's disease (inherited lack of von Willebrand factor or ristocetin cofactor) -- aggregation with ristocetin is usually abnormal in type I disease and increased in type II.

• use of platelet-inhibiting medications (see special considerations)
• autoimmune disorders that produce antibodies against platelets
• myeloproliferative disorders
• uremia (a result of kidney failure)
• acquired storage pool disorder (platelets are no longer effective because of temporary damage, such as in response to cardiopulmonary bypass or vasculitis)
• fibrin degradation products