The evolution in the prioritization for liver transplantation.

Policies for organ allocation can be based on medical urgency, utility or transplant benefit. With an urgency policy, patients with worse outcomes on the waiting list are given higher priority for transplantation [based on the Child-Turcotte-Pugh score or the Model for End-stage Liver Disease (MELD) score, or United Kingdom model for End-stage Liver Disease (UKELD) score]. The MELD and UKELD scores have statistical validation and use objective and widely available laboratory tests. However, both scores have important limitations. Adjustments to the original MELD equation and new scoring systems have been proposed to overcome these limitations; incorporation of serum sodium improves its predictive accuracy and is part of the UKELD score. The utility-based systems are based on post-transplant outcome taking into account donor and recipient characteristics. MELD and UKELD scores poorly predict outcomes after liver transplantation due to the absence of donor factors. The transplant benefit models rank patients according to the net survival benefit that they would derive from transplantation. These models would be based on the maximization of the lifetime gained through liver transplantation. Well-designed prospective studies and simulation models are necessary to establish the optimal allocation system in liver transplantation, as no current model has all the best characteristics.