Control of heparin therapy. Sensitivity of the activated partial thromboplastin time for monitoring the antithrombotic effects of heparin.

Abstract The accuracy of the activated partial thromboplastin time (PTT) test was compared with that of the Lee-White (L-W) clotting test for monitoring the activity of heparin in preventing experimental thrombosis. Following the injection of aged serum as a procoagulant, thrombosis was observed in the clamped external jugular venous segment of 6 of 6 control rabbits. Nineteen of 24 rabbits which had received heparin within 2 hours were protected from thrombosis. The postheparin activated PTT was 52 seconds or greater (normal range=38.0 ± 3.9 seconds) in all 19 (100 per cent) protected rabbits. The postheparin glass L-W clotting time was at least one and a half times the preheparin test in 16 of 19 (84 per cent) protected rabbits. Thus, both the activated PTT and the L-W clotting tests provide an accurate means for monitoring the antithrombotic activity of heparin.