We agree that the implementation of the new international normalized ratio (INR) specific for liver diseases (INR“LD”) will presumably take time and that it is important to work on the different solutions discussed. All the options, namely, specific international sensitivity index for liver diseases provided by manufacturers, certified reference preparation for local calibrations, or well-validated restricted list of recombinant reagent and coagulometers, will require a strong international collaboration between biologists, hepatologists, and industry.
Anyway, we want to emphasize that, whatever the strategy adopted, the INR“LD” must be considered as a new parameter and that its appropriate weight as a variable in all the scores used in liver diseases have to be reassessed in clinical studies. For example, in the MELD (Model for End-stage Liver Disease) score, the relative weight of INR“LD” compared to those of creatinine and bilirubin would probably be higher than the one calculated for the INR obtained with undefined thromboplastins at the time of the score definition.4
Furthermore, we would like to add a comment on the so-called “pragmatic” option proposed by Dr. Tripodi, that is, the centralization of plasma samples in a restricted number of “reference” laboratories for the MELD score calculation. This strategy seems very difficult to implement on an international scale and does not provide the PT standardization needed also in general screening, diagnosis and monitoring of acute and chronic liver injury.5, 6