Which anticoagulant's effects are reflected in the activated clotting time test (ACT)?

The activated clotting time (ACT) test is a critical tool used to assess the anticoagulant effects in patients undergoing certain surgical procedures, particularly those involving cardiopulmonary bypass or other scenarios necessitating heparin administration. Heparin is a direct acting anticoagulant that enhances the activity of antithrombin III, leading to the inhibition of thrombin and factor Xa. This mechanism significantly prolongs the time it takes for blood to clot, which is precisely what is measured by the ACT.

The ACT test is sensitive to the effects of heparin, providing immediate and real-time feedback on the anticoagulation status of a patient. This is essential for monitoring and adjusting heparin dosing during procedures where rapid anticoagulation is necessary.

In contrast, warfarin primarily affects the vitamin K-dependent clotting factors (II, VII, IX, and X) and does not have a direct effect on the activated clotting time. Dabigatran, a direct thrombin inhibitor, and rivaroxaban, a direct factor Xa inhibitor, also have specific tests for monitoring their effects but do not directly correlate with ACT. While additional testing may be required to monitor their activity, ACT remains specifically tailored to measure the anticoagul