The UNOS 'preferential allocation' concept proposal for the allocation of deceased donor kidney transplants: implications for patients with diabetes

Kidney transplantation is highly cost-effective [1] and remains the preferred treatment for end-stage renal disease (ESRD), a condition affecting over half of a million Americans with annual costs exceeding US $25 billion [2]. Transplantation offers a clear survival advantage for qualifying patients compared to dialysis [3]. Unfortunately, the disparity between supply and demand for transplantable kidneys continues to increase. The current waiting list for a kidney transplant now includes over 93 000 patients [4]. In the Scientific Registry of Transplant Recipients 2009 report, there were 10 101 deceased donor kidney transplants and 5966 live donor transplants in 2008, leaving an estimated 76 089 patients still waiting for a transplant [5]. Two patient cohorts, those with diabetes and the elderly, disproportionately contribute to the disease burden of ESRD in the USA. Diabetes causes 44% of new cases of ESRD, >200 000 patients are currently on dialysis or living with a kidney transplant as a result of diabetic nephropathy [2]. The proportion of incident elderly dialysis patients who have diabetes also continues to rise. Between 2000 and 2030, the estimated number of people with diabetes in age groups 45–64 and >65 years will likely double [6]. There is substantial evidence to support kidney transplantation for patients with diabetes. The proportion of diabetic recipients has increased >10-fold since 1970 [7] due to improved care of uremic diabetic patients and higher transplant success rates, particularly early graft survival. Curves of graft survival comparing non-diabetic and diabetic recipients begin to diverge only after ~3 years [7]. Most importantly, as Wolfe et al. [3] demonstrated that the long-term mortality for deceased donor transplant recipients was 48–82% lower compared to patients on the waiting list, with young diabetics experiencing even greater benefit than non-diabetics. In summary, kidney transplantation remains the treatment of choice for diabetic patients with ESRD. Nonetheless, evidence indicates that, for patients with diabetes, the likelihood of being listed for transplant as well as for actually receiving one is less than for other individuals [8, 9]. The result is that patients with diabetes are more likely to die before receiving a deceased donor kidney transplant. The current allocation system for deceased donor kidneys uses a point system determined by waiting time, patient sensitization (anti-HLA antibodies) and tissue matching. Of these factors, the main determinant for allocation is candidate’s waiting time. This is in contrast to lung and liver transplantation policies which focus on reducing mortality in the recipient candidate pool by weighing the severity of a candidate’s condition. In 2011, the Organ Procurement and Transplantation Network proposed a major change to the current 20-yearold kidney allocation policy [10]. The new policy of ‘preferential allocation’ to achieve better survival matching between the donated kidney and its recipient introduces two new metrics to allocation. The first is a kidney donor profile index (KDPI) aimed at identifying the highest quality kidneys [11]. This is coupled with an estimated post-transplant score (EPTS), a measure of a recipient’s predicted life expectancy after transplantation. The EPTS calculation is based on four factors felt to provide a ‘reasonable estimate’ of identifying candidates with the longest post-transplant survival: length of time on dialysis, any prior organ transplant, diabetic status and age. Together, the KDPI and EPTS will be used to match the best 20% of donor kidneys to candidates with the longest expected posttransplantation survival. Afterward, a 30-year age range will be used to allocate the remaining 80% of organs.