Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1128 page)

   Interpretation

Causes of Decreased Values

   
Congenital conditions:

   The prototype for a severe platelet defect (thrombocytopathy) is Glanzmann thrombasthenia, where there is no aggregation with any agonists but positive agglutination with ristocetin.

   Storage pool disease Bernard-Soulier syndrome.

   Abnormal response to ristocetin may be due to von Willebrand disease.

   
Acquired conditions:

   Effect of drugs. Abnormalities in response to arachidonic acid reflect, in most cases, ingestion of aspirin or other NSAIDs

   Myeloproliferative neoplasms and plasmacytic neoplasms with high globulins

   Uremia

   Limitations

   Because of the short functional viability of platelets, the assay must be initiated within 2 hours from blood collection and completed within 4 hours.

   The blood must be kept at room temperature at all times.

   Platelet activation during blood drawing, such as traumatic draws with initiation of clotting, makes the assay invalid. Pneumatic tubes for delivering the blood should not be used.