Screening tests of platelet function: update on their appropriate uses for diagnostic testing.

Global tests of platelet function are often used as screening tests during the laboratory investigation of individuals with suspected hemostatic defects. Because global tests of platelet function do not enable specific diagnosis of platelet disorders, they are normally performed as the first part of a two-step strategy that requires further testing with more specialized assays of platelet function to confirm or refute the diagnosis. The most commonly proposed rationale for testing global platelet function as a first-line investigation is that normal test results may exclude a diagnosis of platelet function disorder so that further specialized testing can be avoided. For this reason, global platelet function tests are usually initially performed at the same time as global assays of coagulation pathway function (prothrombin time and activated partial thromboplastin time, von Willebrand factor screening tests [VWF:Ag, VWF:RCo, and FVIII:C]) and measurement of platelet number. The most widely performed tests for screening platelet function disorders are currently the template bleeding time and the closure time within the Platelet Function Analyzer. These tests will therefore be considered in detail in this review, and we will discuss the limitations of these methods in screening individuals for platelet disorders.