The New Lung Organ Allocation System


By Ramsey Hachem, M.D.

Washington University School of Medicine Barnes-Jewish Hospital
Division of Pulmonary and Critical Care

April, 2005

Next month, the lung organ allocation system will change; this has been a well publicized and somewhat controversial issue.  I will detail the proceedings that led to this new policy and describe the new allocation system in this column.  The current, and soon to be old, algorithm for lung organ allocation was introduced in 1990.  Under this system, lungs are allocated based solely on waiting time after appropriate size and blood group matching, and all potential candidates have the same urgency status.  In 1995, candidates with idiopathic pulmonary fibrosis (IPF) were awarded an additional 90 days when they were listed in response to the perception that they deteriorated more rapidly and were more likely to die waiting for a transplant, than candidates with other lung diseases.  As lung transplantation became a viable option for patients with end-stage lung disease, more patients were listed, and because of the limited supply of donor lungs, waiting times became significantly longer.  In fact, in 1993, over 70% of lung transplant recipients waited less than a year before transplantation; conversely, in 2002, more than 40% of recipients waited over 2 years.  Indeed, many large transplant centers have had expected waiting times well over 2 years.  Obviously, this affected referral patterns, such that many patients were referred for evaluation and listing earlier than necessary in anticipation of a long waiting time.  However, patients with a rapidly progressive disease or those who were diagnosed or referred to a transplant center late in the natural history of their lung disease were significantly disadvantaged by this allocation algorithm since there was no way for the system to account for their clinical condition.  Indeed, while the overall mortality for patients on the waiting list has steadily decreased since the early 1990’s, the underlying diagnosis has had a significant impact on waitlist mortality.  In 1999, there were 30 deaths per 100 patient-years on the waiting list for those with IPF compared with 5 to 10 deaths per 100 patient-years on the waiting list for those with COPD or alpha-1 antitrypsin deficiency emphysema.

Thus, in 1999, the Department of Health and Human Services issued a Final Rule requiring an examination of all organ distribution algorithms to minimize the effects of geography on transplantation and achieve the best use of organs by allocating them to those most in need, while maximizing the utility of organs by avoiding futile transplantation.  The UNOS Thoracic Organ Committee established a sub-committee to examine the current lung allocation system and comply with the Final Rule.  The sub-committee concluded that the current system was flawed because of the growing practice of listing patients before they truly needed transplantation and because of the disparity in waiting list survival among the different lung diseases such that those who could survive the longest on the waiting list had a better chance of transplantation.  In addition, the sub-committee concluded that the ideal system would minimize deaths on the waiting list by considering the underlying diagnoses and physiological and clinical predictors of mortality (such as pulmonary function tests, blood tests, supplemental oxygen requirements, cardiac catheterization data, etc…).  Furthermore, the ideal system should maximize the transplant benefit by considering the expected survival after transplantation for a given patient.  Thus, the sub-committee conducted several retrospective analyses of patients registered on the waiting list over the past several years to identify predictors of waitlist mortality and mortality after transplantation.  The sub-committee analyzed over 4000 patients listed between 1997 and 1998 to determine if data submitted at the time of listing could predict death on the waiting list, and a number of factors were identified for each diagnosis that were associated with an increased risk of death on the waiting list.  Likewise, the sub-committee analyzed over 2000 patients who underwent transplantation between 1996 and 1999 to identify risk factors that would predict death after transplantation.  Based on these results, statistical models were constructed to predict the expected survival (in number of days) without a transplant during an additional year on the waiting list and the expected survival during the first year after transplantation.  In addition, a transplant benefit measure was defined as the expected survival after transplantation minus the expected survival on the waiting list without a transplant.  Thus, a Lung Allocation Score was defined as the difference between the transplant benefit measure and the expected survival on the waiting list without a transplant; this score was then normalized to a continuous scale from 0 to 100.

This new allocation system has some obvious advantages, but like all new policies there are some potential limitations.  In addition to minimizing deaths on the waiting list, a major advantage is that it incorporates assessments of transplant urgency and benefit.  Finally, the system’s impact on transplantation will be reviewed and changes will be amended as necessary over the next few years.