Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (397 page)

   Cardiopulmonary bypass surgery causes marked platelet dysfunction, as well as temporary thrombocytopenia.

   
CBC

   Platelet count may be normal, decreased, or increased, depending on the etiology (see above).

   The peripheral blood smear (PBS) may show normal platelets, or large platelets and thrombocytopenia, depending on etiology.

   Assays for Thrombocytopathies

   Platelet aggregation and release studies with various agonists (ADP, epinephrine, collagen, thrombin, and arachidonic acid) and agglutination studies with ristocetin are presently the best assays to evaluate platelet function. Mixing studies in the presence of ristocetin (the patient’s platelets with normal plasma and normal platelets with the patient’s plasma) are used to differentiate von Willebrand disease type 2b from platelet-type von Willebrand disease (see Table
9-4
).

   PFA-100 is a device used for rapid diagnosis of platelet functional defects.

   The PFA-100 was shown to be sensitive for aspirin-induced defects, Glanzmann thrombasthenia, and von Willebrand disease. If positive, the diagnosis should be refined by studies of platelet aggregation.

   Flow cytometry is a sensitive tool to examine platelet function, but it may not be readily available.

   Electron microscopy may determine the status of platelet granules, but its utility is mostly for research purposes.

Suggested Readings

Kottke-Marchant K, Corocoran G. The laboratory diagnosis of platelet disorders. An algorithmic approach.
Arch Path Lab Med.
2002;126:133–146.

Nurden AT, Flore M, Nurden P, et al. Glanzmann’s thrombasthenia: a review of ITGA2B and ITGB3 defects with emphasis on variants, phenotypic variability, and mouse models.
Blood.
2011;118:5996–6005.

   
DISORDERS DUE TO COAGULATION FACTOR DEFICIENCIES: CONGENITAL CLOTTING DEFECTS

HEMOPHILIA

   Definition