A modified international normalized ratio as an effective way of prothrombin time standardization in hepatology

International Normalized Ratio (INR), which standardizes prothrombin time (PT) during oral anticoagulation, has been extended to standardize PT in liver diseases and is included in prognostic models such as the Model for End stage Liver Disease (MELD). However, mechanisms of PT prolongation in liver diseases differ from those involved in oral anticoagulation, and the thromboplastin reagents differ in their sensitivities to these 2 mechanisms. Our aim was to determine whether, in the calibration model for thromboplastins proposed by the World Health Organization, the use of plasmas from patients with liver diseases instead of plasmas from patients on oral anticoagulation could lead to a new INR specific for liver diseases (INR "LD"), achieving a real standardization of PT. First, 5 thromboplastins were calibrated against an international reference using 60 plasmas of patients with liver failure and, in a second step, the variation of PT reported as seconds, the ratio of patient PT to normal PT, INR, and INR"LD" was assessed in 34 other patients. MELD scores were calculated with the INR values obtained with the 5 thromboplastins. Only INR"LD" eliminated variability in PT results observed with the different thromboplastins. The discrepancy between MELD scores were up to 4 and 7 points in 52% and 17% of the patients, respectively. Conclusion: INR "LD" may provide a common international scale of PT reporting in hepatology. Its adoption would be an important step because of the significant impact on MELD score induced by interlaboratory variability in INR determination.