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
Either venous or capillary blood can be used to monitor anticoagulation therapy. 2 To produce a result, thromboplastin is added to the blood sample to activate coagulation.2 This causes a blood clot to form. The time it takes for this clot to form is measured in seconds and is known as the PT. 2