[Control of oral anticoagulation. Current concepts].

The main objective of this short review is to bring into focus the most relevant of the recent advances in prothrombin time standardization and analyze the recommendations of the World Health Organization (WHO) for monitoring patients with thrombotic disorders under treatment with oral anticoagulant drugs. The prothrombin time (PT) is indicative of the proper therapeutic range in patients receiving oral anticoagulant drugs; however the reliability of the results will depend on the source and nature of the thromboplastin used. Different normal and therapeutic rangers are frequently observed when different brands of thromboplastin reagents and/or methods are used. The WHO, in conjunction with the International Committee of Thrombosis and Hemostasis and the International Committee of Standardization in Hematology, has recommended a calibration scheme for thromboplastin standardization with special reference for anticoagulant monitoring. Instead of reporting patient values, either in seconds or percent activity, WHO recommends the PT results in terms of an international normalized ratio (INR). This is obtained by formula: INR = RC in which R is the patient's PT and C is the international sensitivity index (ISI) of the thromboblastine employed. The INR represents the PT that would be obtained if it were performed with the WHO thromboplastin reference preparation. We suggest that these new concepts should be implemented by both laboratory and clinical professionals with the purpose of improving the effectiveness and safety of oral anticoagulation.