Critical appraisal, clinical usefulness, and implementation of the thromboplastin concept of prothrombin-time standardization.

The thromboplastin concept of standardization of the prothrombin-time according to Biggs and Denson survived criticism, obtained support from many countries, and recently proved to be applicable in the clinical practice of monitoring long-term oral anticoagulation of the individual patient. Reference thromboplastins certified by the Bureau Communautaire de Reference of the European Economic Communities are now being produced, to be used in calibration by manufacturers of thromboplastin preparations. Assayed normal and abnormal plasmas will enable both manufacturers and clinical laboratories to implement the thromboplastin concept in the practice of prothrombin-time standardization. The present basic World Health Organization reference thromboplastin human combined (preparation 67/40 of the British National Institute for Biological Standards and Control) is, for various reasons, supposed to be replaced by a thromboplastin human plain (a batch of British Comparative Thromboplastin) as soon as it becomes available and has been approved. Expression of the coumarin induced coagulation defect in terms of International Calibrated Ratios in addition to conventional terms will greatly facilitate understanding individual patient results as well as optimal therapeutic ranges to be aimed at. To create, for stability checking of reference thromboplastins and reference plasmas, stable reference points, unmistakable quantification of the coumarin-induced enzyme defect is mandatory.