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International and national standardization of control of anticoagulant therapy in patients receiving coumarin and indanedione drugs using calibrated thromboplastin preparations.

In most parts of the world anticoagulant therapy with coumarin drugs is controlled by the one-stage prothrombin time test, and because of different sensitivities of the methods to the coumarin defect and different methods of reporting the results, there is difficulty in comparing the level of anticoagulation at one centre with that at another. The provision internationally of a reference preparation of thromboplastin is an attempt to provide a means whereby the degree of anticoagulation determined at different centres may be compared and therapy more uniformly controlled. A research standard of thromboplastin, human (67/40) is obtainable, with information about it, on application to the Division of Biological Standards, National Institute for Medical Research, Mill Hill, London. (This is a freeze dried preparation which is stable and which has been characterized in an international collaborative study by Bangham, Briggs, Brozovic, and Denson, 1970.) This could be used by laboratories to calibrate their own thromboplastin preparations. It is hoped further that national reference thromboplastin preparations will be made and calibrated with this research standard2 and that commercial preparations should be similarly calibrated against the national reference preparations. This would enable better control of therapy in individual patients, particularly for patients travelling from one hospital to another or travelling abroad. In addition, information obtained from patients included in a clinical trial at different centres should be comparable if the clotting time ratios are expressed in terms of the national or international reference preparations.