Laboratory observations and clinical implications of monitoring the effect of heparin by bioassay.

Laboratory and clinical experience in the monitoring of circulating heparin concentration of bioassay shows that the whole blood clotting time and the activated partial thromboplastin time differ in their reflection of the state of anticoagulation. The decay of biologic activity may be as short as 30 minutes in one patient or as long as 360 minutes in another. This fact may drastically affect patient response to the drug. Safe and rational clinical heparinization is dependent upon periodic monitoring of the circulating heparin concentration. The success of this method was illustrated in two representative patients.