Progress report: the activated coagulation time of whole blood (ACT).

The activated coagulation time of whole blood (ACT) has, in the nearly ten years since its first description in the literature, proven itself one of the best laboratory tests for the control of heparin therapy, both for patients undergoing treatment for thromboembolic disease and for those on extracorporeal circulation. It is simple, largely free from subjective variation, precise, and quick. Prolongation of the ACT in the heparinized individual is directly proportional to the concentration of heparin in the blood, and the test accurately reflects the semilogarithmic disappearance of the anticoagulant effect in most patients. In addition, the test serves well as a bedside screening test for deficiencies of the intrinsic coagulation mechanism. The author summarizes the sutdies that have been carried out on this technic since its original description, and briefly presents three protocols for heparinization of patients who have thromboembolic disease.