[Biological monitoring of treatment with antivitamin K. Value of INR and definition of new therapeutic ranges. A study of 73 patients].

The prothrombin time test (PT) is the most common method used for monitoring oral anticoagulant therapy. As a consequence of the variability in responsiveness of different thromboplastins, PT results obtained from patients on oral anticoagulant therapy may not be interchangeable between laboratories and as consequence could produce potential problems for anticoagulant control. The conversion of PT in INR (International Normalized Ratio) has been introduced recently to standardise the PT used for anticoagulant control. 127 determinations of prothrombin time and INR with 2 different thromboplastin reagents (Thromboplastin C Dade and Owren reagent) have been performed in 73 patients. This study confirm the usefulness of the INR (INR discrepancy in 10% of the cases) despite the imperfections concerning the choice of the control plasma and the need of a precise measurement of the ISI, International Sensitivity index. In parallel, changes in therapeutic ranges for anticoagulant therapy occurred, based on results of the international literature: less intense anticoagulant treatment (INR 2-3) is effective against recurrent venous thromboembolism with reduced bleeding. Different therapeutic ranges must be recommended for oral anticoagulant therapy according to the indication of the treatment.