Proteins secreted by platelets: significance in detecting thrombosis.

Because platelet survival measurements are time-consuming and may not completely reflect platelet involvement in hemostasis and thrombosis, other tests have been sought. Measurement of two proteins released by platelets, platelet factor 4 (PF4) and beta-thromboglobulin (betaTG), may provide simpler, more direct means of quantitating platelet involvement. The radioimmunoassays for these proteins reviewed in this paper are sensitive and specific. Although there are technical problems still to be resolved in their clinical application, clinical studies to date suggest that such assays will be useful in studying the pathogenesis and course of thromboembolic disorders. PF4 and betaTG levels apparently do reflect in vivo platelet release. Because release of PF4 and betaTG parallels release of platelet-derived growth factor, plasma PF4 and betaTG levels should also reflect release of that protein. The PF4 and beta TG assays along with an assay for fibrinopeptide A in clinical samples should help elucidate the relative importance of platelet release and fibrin formation in thromboembolic disorders.