Invited letter in response to: “Is the kidney donor profile index (KDPI) universal or UNOS-specific?”

Graft survival in 37 recipients of 1 or 2 histologically evaluated kidneys from octogenarian donors with a kidney donor profile index (KDPI) of 96% to 100% was similar to that observed in 198 recipients of non–histologically evaluated single grafts from donors younger than 60 years with a KDPI of 0% to 95%.1Ruggenenti P Silvestre C Boschiero L et al.Long-term outcome of renal transplantation from octogenarian donors: a multicenter controlled study.Am J Transplant. 2017; 17: 1-13Abstract Full Text Full Text PDF Scopus (38) Google Scholar Ekser and coworkers2Erksin B, Powelson JA, Fridell JA, et al. Is the kidney donor profile index (KDPI) universal or UNOS-specific? [published online ahead of print 2017]. Am J Transplant. https://doi.org/10.1111/ajt.14538.Google Scholar consistently reported a 5-year graft survival rate of 91% in 100 recipients of dual transplants of histologically evaluated kidneys from donors older than 60 years with cerebrovascular death and a KDPI of >85%. Thus, these 2 studies, as well as previous reports in a similar context,3Remuzzi G Cravedi P Perna A et al.Long-term outcome of renal transplantation from older donors.N Engl J Med. 2006; 354: 343-352Crossref PubMed Scopus (414) Google Scholar converge to indicate that kidneys from donors older than 60 years with a KDPI of >85% can safely be used, provided the kidneys are selected and allocated on the basis of pretransplantation histologic findings. However, according to United Network of Organ Sharing (UNOS) data, only 11% of kidneys from donors with a KDPI of >85% are used for transplantation, and their 5-year survival approximates only 50%.4Rege A Irish B Castleberry A et al.Trends in usage and outcomes for expanded criteria donor kidney transplantation in the United States characterized by kidney donor profile index.Cureus. 2016; 8: e887PubMed Google Scholar Ekser and coworkers2Erksin B, Powelson JA, Fridell JA, et al. Is the kidney donor profile index (KDPI) universal or UNOS-specific? [published online ahead of print 2017]. Am J Transplant. https://doi.org/10.1111/ajt.14538.Google Scholar hypothesized that the KDPI score might not be adequate for predicting graft outcomes outside of the UNOS context. Indeed, the aforementioned studies were from Italy and included mostly white donors, whereas the KDPI score has been implemented on the basis of data from donors of different ethnicities. However, when we evaluated the relative weight of ethnicity in the KDPI score (https://optn.transplant.hrsa.gov/resources/allocation-calculators/kdpi-calculator/), we found that the KDPI, and corresponding kidney donor risk index (KDRI), of a prototype 63-year-old donor (height 180 cm, weight 90 kg) without risk factors additional to age who died from a cerebrovascular event were 85% and 1.46 for all considered ethnicities, with the exception of black donors or donors of African origins whose KDPI and KDRI were remarkably higher (94 and 1.74, respectively). However, only 14% of deceased US donors are black or of African origin (http://optn.transplant.hrsa.gov/), and their relative weight in the Organ Procurement and Transplantation Network (OPTN) algorithm is consequently low and cannot, per se, explain the nongeneralizability of the KDPI score. On the other hand, donor age might have excessive relative weight in the algorithm. Indeed, the KDPI of our average (white) donor increased progressively from 85% at the age of 63 years to 95% at the age of 72, and plateaued at 100% by the age of 81. The KDRI increased progressively between the ages of 60 and 90 (Figure 1). Thus, independently of concomitant risk factors, any >63-year-old donor would have a KDPI of >85% and therefore the kidneys would be discarded in almost 90% of cases.4Rege A Irish B Castleberry A et al.Trends in usage and outcomes for expanded criteria donor kidney transplantation in the United States characterized by kidney donor profile index.Cureus. 2016; 8: e887PubMed Google Scholar As suggested by Ekser and coworkers,2Erksin B, Powelson JA, Fridell JA, et al. Is the kidney donor profile index (KDPI) universal or UNOS-specific? [published online ahead of print 2017]. Am J Transplant. https://doi.org/10.1111/ajt.14538.Google Scholar this major limitation could be addressed by selecting and allocating older kidneys on the basis of biopsy findings. With this approach, the donor pool could be expanded without affecting transplant outcomes. On the other hand, age-related histologic changes in kidneys from donors healthy enough to survive for 80 years or longer could reasonably be less severe than those in younger donors who died prematurely of a cerebrovascular insult. In this latter category—if one excludes patients who died of cerebrovascular abnormalities—risk factors, including smoking, the abuse of certain drugs, obesity, hypertension, and/or diabetes, may well have had a negative impact on the kidney. Considering the strong link between cerebrovascular and renal disease,5Lee M Ovbiagele B Reno-cerebrovascular disease: linking the nephron and neuron.Expert Rev Neurother. 2011; 11: 241-249Crossref PubMed Scopus (17) Google Scholar a preimplantation kidney biopsy might be even more strongly indicated in relatively young donors than in octogenarians. The success of transplantation could be further improved by evaluating the viability of marginal kidney via pulsatile perfusion (Pulsed Perfusion for Marginal Kidneys [PREDICTION]; https://clinicaltrials.gov/ct2/show/NCT02055950?term=pulsatile+perfusion&cntry1=EU%3AIT&rank=2, accessed November 30, 2017), matching recipient to donor age, and carefully evaluating recipient risk factors. As for the importance of the pretransplantation renal biopsy for selecting an allocated kidney donor, we must not forget that we are supposed to transplant nephrons, rather than kidneys! The authors of this manuscript have no conflicts of interest to disclose as described by the American Journal of Transplantation.