[Quality control of ISI/INR system in oral anticoagulant therapy]

Ten controlled plasmas and 4 thromboplastin reagents were distributed to 75 laboratories for measurement of prothrombin time (PT). The results were converted to prothrombin activity (PA). prothrombin ratio (PR) and international normalized ratio (INR). Among the 4 different ways of expression, the discrepancy between the results obtained by the different reagents was the smallest when the results were expressed by INR. However, the discrepancy of the results was still remained because of the different assay methods used routinely at these laboratories, even with the use of ISI/NR system (Instrumentation effects). In this study, reference curve of prothrombin time: INR was created using INR reference plasmas, which were selected from commercial control plasma using a standard thromboplastin reagent. INR's of 108 patients' plasmas were calculated by ISI/INR system on one hand, and by the use of the reference curve of the prothrombin: INR on the other hand. It was found that the discrepancy of the results obtained by different assay methods was significantly improved by the latter method, compared to those obtained by the conventional ISI/INR system.