The new liver allocation system in the United States was implemented on February 27, 2002. The rationale for moving to this new system was based on the recognition that waiting time was a poor criterion on which to prioritize liver transplant candidates, because it had little relationship to liver-related mortality.1 In addition, there was widespread dissatisfaction with the more traditional measures of liver disease severity because they included subjective clinical variables that were subject to manipulation and not standardized. This new system was developed using an evidence-derived model, the model for end-stage liver disease (MELD),2, that provided a much more objective measure of short-term liver disease–related mortality. In development of this new policy, the MELD score was validated against several different cohorts of patients, with and without inclusion of the subjective clinical variables, and proved to be consistent and highly predictive of 3-month mortality.3, 4 However, policymakers recognized that not all appropriate liver transplant candidates had a high risk of death even though they may have had an increased urgency for transplantation. This is most apparent for candidates with early-stage hepatocellular carcinoma. For this reason, an alternative pathway for prioritization was developed utilizing a regional peer-review process through regional review boards. This process allows candidates who are thought to have urgency greater than that assigned by their calculated MELD score to receive higher priority with peer approval.5
Initial results for this new system have been encouraging. Since its implementation, fewer inappropriate patients have been placed on the waiting list, and there has been a trend toward reduced waiting list deaths and statistically significant increases in transplantation rates.6 Candidates with hepatocellular cancer were initially given increased priority based on an estimated risk of progression beyond stage II disease. In retrospect, these approximations overestimated this risk, and a subsequent adjustment in the priority score for hepatocellular carcinoma candidates has been made. The adjustment reduced the probability of transplant and increased the probability of remaining on the list, but it did not increase the dropout rate for these patients. Patients granted increased priority by regional review boards have had a higher probability of transplant than the standard MELD candidates. An increasing number of children have been transplanted at the status 1 designation, with many of them having chronic liver disease. Early posttransplant survival rates have been excellent,6, 7 with no apparent increase in liver transplant costs, at least in one recent study.8
Future directions for policy development and improvement include revisions to the status 1 definitions for pediatric and adult patients, refinements in the liver distribution units, plans to make the peer review process more uniform, and assessments of nonmortality end points.