Prothrombin time
Prothrombin time (PT) is the primary method used in monitoring oral anticoagulant therapy. The prolongation of PT depends on reductions in three of the vitamin K dependent clotting factors (II, VII and X).1,2 Changes in the PT noted in the first few days of vitamin K antagonist (VKA) therapy are primarily due to reductions in factor VII which has the shortest half-life of 6 hours. The reduction of factors X and II subsequently contribute to prolongation of the PT. 2