Anesthesiology and Intensive Care

The activated clotting time (ACT) is a point-of-care test most commonly used to monitor for heparin effect during cardiovascular surgery. The test consists of adding whole blood to a test tube most often containing either diatomaceous earth (celite) or kaolin. These particulate activators induce thrombus formation, which is timed. Normal ACT values range between 80 and 120 seconds. The ACT test is useful in that it uses whole blood, can be performed easily at the point of care, and provides results relatively quickly. It is important to realize, however, that ACT is a nonspecifi c test of coagulation. That is to say, a prolonged ACT can be caused by almost anything that decreases coagulation, not just heparin . While ACT is most affected by the state of the intrinsic coagulation system, the extrinsic system and platelet function also play a role. Therefore, heparin, warfarin, platelet dysfunction, protamine excess, and hemodilution would all be expected to increase...