Clotting, activated partial thromboplastin and coagulation times in monitoring heparin therapy.

The automated-activated coagulation time, manual-activated coagulation time and the activated partial thromboplastin time were compared to the whole blood clotting time in the measurement of hypocoagulation of heparinized blood. The normal ranges and degree of reproducibility were determined for each clotting assay. Each method was examined for its sensitivity to various concentrations of heparin. In addition, blood samples from patients treated with heparin were assayed by all four methods and their results were compared. The results indicated that the manual-activated clotting time correlated best with the whole blood clotting time, was sensitive to low concentrations of heparin, formed a discernible clot within a convenient time period in blood containing high concentrations of heparin, was reproducible and was easily performed.