Platelet Aggregation

With regard to normal findings, results depend on the platelet agonist employed, ^[1]  with the reference range being a normal biphasic pattern of aggregation in response to specific platelet activators (see image below).

Aggregation curve showing events in classic biphasic aggregation.

Decreased platelet aggregation may be associated the following:

• Autoimmune disorders that produce anti-platelet antibodies

• Bernard-Soulier syndrome

• Fibrin degradation products

• Glanzmann thrombasthenia

• Drugs that block platelet formation (eg, thiazide diuretics, interferon, alcohol)

• Myeloproliferative disorders

• Uremia

• von Willebrand disease

Specifics for collection and panels are outlined as follows:

• Specimen type: Whole blood

• Container: Vacutainer, light blue (citrate)

• Collection method: Venipuncture

• Specimen volume: 4 mL

Other instructions

See the list below:

• Four tubes are needed for platelet aggregation testing.

• Seven tubes are required for full aggregation and secretion testing.

• Process whole blood specimens within 4 hours of collection.

• Store specimens at room temperature (cooling may lead to activation).

Related tests: Complete blood count, platelet count, prothrombin time (PT); partial thromboplastin time (PTT), bone marrow biopsy, coagulation factors, von Willebrand factor (VWF)

Description

Platelet aggregation studies test the clumping response of platelets to various platelet activators (eg, ADP, collagen, arachidonic acid, thrombin, epinephrine, ristocetin) as continuously recorded by a light transmission aggregometer. With some aggregometers, the secretion of platelet granules, another indicator of platelet function, may also be evaluated simultaneously by measuring the release of ATP by the aggregating platelets. Platelet secretion defects can provide greater diagnostic sensitivity than platelet aggregation testing alone. ^{[2, 3, 4]}

Indications/Applications

Conditions associated with decreased platelet aggregation include suspected hereditary and acquired disorders of platelet function. Indications for platelet aggregation studies include the following:

• Diagnostic evaluation of excessive bleeding or bruising

• Monitor the effectiveness of antiplatelet medication

• Detect aspirin resistance

• Monitor platelet function during complex surgical procedures

• Screen at-risk presurgical patients

Considerations

Medications (including over-the-counter medications) that may affect platelet aggregation results include the following:

• Antibiotics (penicillins, cephalosporins, nitrofurantoin)

• Antihistamines

• Aspirin ^[5]

• Aspirin-containing compounds

• Clopidogrel ^[6]

• Dipyridamole

• Nonsteroidal anti-inflammatory drugs (NSAIDs)

• Theophylline

• Ticlopidine

• Tricyclic antidepressants

Healthcare providers should ask patients about any of these medications that may have been taken within 2 weeks before testing.