Allocating organs has always been the most contentious issue in the field of transplantation. Which patient should get an organ from the limited supply available has been regulated, debated, modeled, and revisited for as long as transplants have been performed. Historically, fairly simple "point" or "status" systems were used, relying heavily on the judgement of individual physicians and centers and on waiting time. As part of the 2000 Final Rule, the OPTN was charged with creating systems that would rely more heavily on measurable laboratory criteria and place a priority on transplanting the sickest patients first.
The first "modern" allocation system was the MELD (Model for End-Stage Liver Disease) and PELD (Pediatric End-Stage Liver Disease) systems for allocating livers. These are fairly simple systems based on a few variables, with scores that are designed to roughly correlate with the chance of death from liver failure. These systems did provide a degree of objectivity to liver allocation, but their implementation was complicated by the fact that patients with some diseases (such as metabolic diseases and liver cancer) may have a need for transplantation that is not reflected by the variables in MELD/PELD, which are based on cirrhosis. Revisions of the MELD system for patients with hepatocellular carcinoma and a fairly high proportion of "exceptions" from regional review boards (RRBs) for pediatric candidates have been needed, so it's still unclear how fully the system has reached its goals.
A new lung allocation system, based on a simply-named but mathematically-complicated Lung Allocation Score (LAS) went into effect in May 2005. The LAS attempts to predict the one-year survival of candidates without a transplant and with a transplant. Those that have the greatest difference between these scores will presumably have the greatest benefit, and therefore get the greatest priority. The LAS has dozens of variables, which vary based on the disease type, and appears to encompass everything important in organ allocation. Ironically, the most elaborate system currently in place replaces what was previously the most simple--lungs used to be allocated based solely on waiting time, a pure waiting list. Despite its complexity, or maybe because of it, the LAS appears to be very successful, having reduced waiting times and deaths on the waiting list. The New York Times recently chronicled the success of the new system and the failure of the old one.
Kidneys are next. The waiting list for kidney transplantation is by far the largest, accounting for the most patients, the longest waiting times, and the greatest absolute number of deaths while waiting. Each of these is a unique issue for the kidney transplant community, bringing up several questions:
- Should older patients get kidneys from younger donors?
- How should "marginal" kidneys be used to the greatest benefit?
- In a system where the average waiting time approaches four or five years, does a system that gives one person a kidney within one or two years mean that someone else will have to wait nine or ten years?
- How should racial and ethnic disparities be limited?
These issues were covered in a New Year's Day front page story in the San Francisco Chronicle, and in a much more personal documentary by the Los Angeles Times.
It appears that a new kidney allocation system will resemble the lung system, calculating a "Net Lifetime Survival Benefit" for transplantation. Some of the current thinking of policymakers is reviewed on the UNOS Kidney Transplantation Committee web site. UNOS will also be holding a Public Forum on the revisions of the kidney allocation system, looking to inform and seek input from patients in the kidney transplant community. Clearly, this issue is a vital one in transplantation today and in the future.