β -Thromboglobulin and Platelet Survival in Patients with Arterial Thromboembolic Disease

Abstract

A previous study has reported raised plasma levels of a platelet specific protein β-thromboglobulin (β-tg) in some patients with arterial thromboembolism (AT), rheumatic heart disease (RHD) and prosthetic cardiac valves (PCV). Comparative studies of β-tg levels and platelet survival are now reported in similar patients. β·tg was measured by a radioimmunoassay and platelet survival using 51Cr labelled autologous platelets. In normal individuals a correlation (r=0.9l) has been demonstrated between the reciprocal of the plasma β-tg concentration and the platelet survival. In 5 patients with AT the mean platelet lifespan was 7.4 days (range 5.7-9.3) and this was similar to 7.9 days (5.5-10.3) in control subjects. The mean plasma β-tg concentration in the patients, however, was 108ng/ml (range 45-235) and this was significantly greater (p=0.05) than 30ng/ml (range 17-72) in normal individuals. To determine if a single measurement of β-tg is representative of subsequent estimations in patients with RHD and PCV, samples were collected at monthly intervals from normal subjects and patients. In 11 patients the mean level was 50ng/ml and the coefficient of variation of repeat samples was 28% (range 13-68), while in normals the mean plasma concentration was 19ng/ml with a coefficient of variation of 26% (range 13-48). Treatment with dipyridamole resulted in decreased levels of plasma β-tg in some patients. It is concluded that in normal subjects and in patients with RHD and PCV the plasma β-tg is remarkably constant. It is suggested that the plasma β-tg concentration may be a more sensitive index of platelet activation than shortening of the platelet mean lifespan.