The international normalized ratio to prioritize patients for liver transplantation: problems and possible solutions

Summary.  The prothrombin time (PT) test once designed by Dr Quick to investigate patients with obstructive jaundice was later adapted and standardized by means of the international normalized ratio (INR) to monitor patients on treatment with vitamin K antagonists (VKA). After more than 70 years from its introduction it is now time to think about its standardization for those very patients for whom it was intended at the beginning of its history. Two studies carried out independently and published recently in the same issue of a specialized journal do exploit the very same idea on how to accomplish this standardization. Both of them confirm previous anecdotal observations that the INR as devised for patients on VKA (INR_vka) is not valid to harmonize PT results for patients with chronic liver disease. This fact, that at first sight may appear academic, has important consequences because the PT INR is used to construct the model for end-stage liver disease (MELD) scores, which is widely used to prioritize patients for liver transplantation. The two studies further demonstrate that an alternative calibration model, modified from that recommended by the World Health Organization for patients on VKA, may be feasible also for patients with chronic liver disease. This alternative calibration model, which calls for the substitution of plasmas from patients on VKA with those from patients with chronic liver disease, may be highly beneficial to harmonize the calculation of the MELD score, with important implications for the prioritization of patients for liver transplantation.