The mismatch between supply and demand of deceased donor kidneys for transplantation continues to grow. There are a number of ongoing initiatives to address the donor shortage, including efforts to increase the overall number of organ donors as well as to improve utilization of the current organ donor pool. When it comes to utilization of marginal deceased donor kidneys, transplant clinicians and patients alike face a difficult challenge. When contemplating an offer from a marginal donor, the question to patients and their transplant team is, will this kidney function well enough and long enough to provide both a survival benefit and a quality of life advantage over dialysis?
To help answer this question, a system of classifying deceased donor kidneys according to quality was implemented in 2002, with each kidney donor being labeled as either a standard criteria donor (SCD) or expanded criteria (ECD) donor. On average, ECD kidneys tend to have a statistically higher risk of graft failure at 1 year based upon clinic donor factors such as age, terminal renal function and presence of comorbidities such as hypertension or death from cerebrovascular accident (1). With time and experience the binary SCD/ECD classification system has been shown to misclassify kidneys in both directions—some kidneys labeled as ECD perform well, while some kidneys labeled as SCD do poorly. To improve upon this schema, Rao et al. developed a Kidney Donor Risk Index (KDRI) that classifies all kidneys across a continuum of risk based on ten donor factors (2). The KDRI is an estimate of the relative risk of post-transplant kidney graft failure (in an average, adult recipient) from a particular deceased donor compared to a reference donor. The Kidney Donor Profile Index (KDPI) is derived by simply ranking all donors on a scale of 0–100% based on their KDRI (lower KDPI numbers indicate lower risk of graft failure). Figure 1 reveals that the relative risk of graft failure increases only incrementally as KDPI increases until KDPI reaches around 90%, after which the risk increases more sharply.
In this issue of American Journal of Transplant, Woodside et al. examine the utilization of kidneys from SCD and ECD donors with similar KDRI values to determine the effect of the ECD/SCD label (3). Using data from the Scientific Registry of Transplant Recipients from November 2002 until May 2010, the authors focused on a group of donors with KDRI 1.4–2.1 that included both SCD and ECD kidneys. They found that overall, ECD kidneys had a higher rate of discard. However, when they looked at donors based on three KDRI intervals (1.4–1.6, 1.6–1.8 and 1.8–2.0), SCD and ECD kidneys within the same KDRI interval had similar rates of transplantation. Also importantly, although ECD kidneys overall had worse graft survival compared to SCD kidneys, there were no differences in graft survival within KDRI intervals. So for example, kidneys from donors with KDRI 1.8–2.0 had similar outcomes whether they were labeled SCD or ECD.
In March 2012, the OPTN began including the KDPI along with the SCD/ECD classification for donors in DonorNet® at the time of organ offers to assist in assessing the quality of deceased donor kidneys. Eventually, the OPTN Kidney Committee intends to use KPDI as an allocation tool in the new kidney allocation system. The KPDI will be used in “longevity matching” which aims to match the longevity of a kidney with the estimated posttransplant survival of a small subset of waitlist candidates. The goal of longevity matching is to maximize the number of life years lived with each donated organ, while minimizing life years lost following death with a functioning graft. The work of Woodside et al. adds to the evidence supporting the use of KDPI in education and allocation. Ultimately, KDPI is a metric of aggregate risk and a decision about the appropriateness of a kidney offer must be made with patient characteristics and preferences in mind. To date, we have data like that presented by Woodside et al. that validates the performance of KDPI as a prediction tool. What is not known is how KPDI will affect behavior now that it is readily available at the time of offers. And while no one metric is a perfect prediction tool, the KDPI will allow us to make more informed choices about deceased donor kidney offers. This will potentially increase kidney utilization for the appropriate recipients, while maximizing outcomes for our increasingly diverse and ever expanding recipient pool.