Evaluation of the activated whole blood clotting time (ACT) in vitro.

The activated whole blood clotting time (ACT) was analyzed in vitro using blood samples from normal individuals and from patients with heart disease, scheduled for open heart surgery. The ACT was found to be normally distributed in a group of normal individuals with a mean of 135 sec. In patients with heart diseases, the average ACT was slightly shorter than in normal individuals. A linear relationship between ACT and heparin concentrations was established. Haemodilution and depletion of platelets did not significantly influence the ACT. When a clean venipuncture with disposable needles is used, ACT is a reliable, uncomplicated bedside technique by which heparinisation can be monitored.