Laboratory monitoring of oral anticoagulant therapy.

The safety and success of oral anticoagulant treatment are dependent on laboratory control by the prothrombin time test. Until recently, the therapeutic range in prothrombin ratios of 2.0 to 2.5 resulted in greatly different dosage regimes, because of the lack of standardization of the test, particularly its thromboplastin component. Low-dose warfarin was associated with responsive thromboplastin. In North America and many other countries, a high-dose regime from high international sensitivity index thromboplastin caused more bleeding.