INTRODUCTION
Kidney transplantation (KT) confers better survival than remaining on dialysis.1 The general benefit of KT has been confirmed using kidneys from expanded criteria donors, including elderly donors, as well as recipients with comorbidities.2-5 In recent years, both the increase in age and life expectancy among incident patients on dialysis have led to an expansion of the acceptance criteria for kidney donors4-7 and transplant recipients.5 In Catalonia, nearly half of new patients in renal replacement therapy (RRT) are older than 70 years, and more than half of donors are over 60 years old.8
Practice guidelines from the major medical societies support transplantation of older patients with end-stage renal disease (ESRD).9-11 However, they recommend that older candidates should be screened more carefully for cardiovascular disease and malignancy9 and recognize that age-related comorbidity is an important limiting factor.11
Stretching the limits in terms of age or comorbidity both in donor and recipient has an unavoidable impact in patient and transplant outcomes.7,12 Some studies that compared outcomes among KT recipients and patients who remained waitlisted on dialysis pointed to a higher mortality risk during the first weeks after transplantation, especially when older donors were considered or recipients had comorbidities.2,8 On the contrary, older patients on dialysis are increasingly being accepted for KT in many transplant units because of the reasonably good outcomes, even in those older than 80 years.13 However, in a normal scenario, patients over 70 or 80 years old do not usually receive optimal kidneys, and the old-for-old allocation system might imply higher risk for older patients. Our group has previously reported a survival benefit when comparing patients who received a kidney from a donor ≥65 years3 or ≥75 years4 to waitlisted patients who remained on dialysis.
The increased percentage of donors >80 years registered in recent years in Spain14 encouraged us to investigate the outcomes with KT from these donors, which are consistently discarded in other countries.15 We also aimed to focus on the outcomes in older recipients to clarify the real potential benefit obtained with these organs. Therefore, we investigated the survival benefit using kidneys from extremely old donors aged ≥80 years, in old recipients, as well as which factors might be implicated in a worse patient prognosis. In particular, we were interested in determining which patients would not benefit from receiving those extremely aged kidneys. We studied ≥60 years old patients who started RRT and joined the transplant waiting list. By means of a time-dependent nonproportional survival analysis, we assessed KT outcomes from very elderly deceased donors (80+ y). We also evaluated whether the benefit of the KT varied per different patient features and aimed to establish a potential interaction between recipient age and the fact of being transplanted to assess whether this benefit mitigates over time.
MATERIALS AND METHODS
Study Design and Patients
We used data from the Catalan Renal Registry (RMRC), which is a mandatory population-based registry covering 7.5 million people that collects information on all patients with ESRD requiring RRT in Catalonia. At the moment of starting RRT and at every switch of treatment throughout RRT, a registration form is filled in. Every year an update has to be carried out and sent to the RMRC up to the finalization of RRT, death of patient, or loss to follow-up. A double control check is performed by a team of professionals who work in collaboration with mortality, invoice registries, and dialysis hospital registries. All dialysis and KT patients receive permanent full public medical coverage, including all medications. From 1990 to 2014, a total of 22 821 patients began treatment for ESRD in Catalonia.
Patients were selected according to the following inclusion criteria: patients ≥60 years who started dialysis (n = 14 947) and joined the transplant waiting list for the first single deceased KT in 1990 to 2014 (n = 2585). From those patients, (1) 67 received a dual KT (3 from donors younger than 60 years, 62 from donors aged between 60 and 79 y, and 2 from donors ≥80 y); (2) 373 received a KT from a donor younger than 60 years; and (3) 1212 received an organ from a donor older than 60 years (1084 received from a donor aged between 60 and 79 y and 128 from a donor aged ≥80 y). We excluded patients who received a living donor KT (n = 77), as in Catalonia those patients are not usually on the KT waiting list. We also excluded patients who were waiting for multiorgan transplantation because they were on a different waiting list (n = 9).
We also analyzed discarded kidneys from donors ≥80 years old between years 2000 and 2014 (n = 185) and the causes of discard.
RMRC follows all the principles in the World Medical Association Declaration of Helsinki, only relying in the official center database. As a mandatory population-based registry, data were obtained retrospectively, and no informed consent or institutional ethics board review was required.
Statistical Analysis
Transplant Outcomes
We assessed kidney graft survival defined as period from transplant date up until graft loss or patient death, or the end of the study observation (December 31, 2016), whichever came first, among 1212 recipients who received a first single KT from a donor ≥60 years old. The median follow-up was 4 years, with a maximum of 21 years. In this cohort, we calculated the cumulative incidence competing risk functions, which were used to calculate unadjusted incidence of 5-year graft survival, considering patient death with functioning graft as a competing event.16 We also calculated adjusted risk of patient death with functioning graft and adjusted risk of graft loss by means of competing-risks regression, considering both graft failure and patient death with functioning graft as a competing event. Transplant outcomes were compared in 2 donor age groups, 60 to 79 years versus ≥80 years.
Donor variables considered were age, sex, and cause of death. Recipient variables considered were age at the time of transplantation, sex, cause of ESRD, HCV serology, maximum panel reactive antibody (PRA), time on dialysis before KT, having at least 1 of the 5 cardiovascular comorbidities (ischemic heart disease, cardiac failure, cardiac conduction disorders, cerebrovascular disease, peripheral vascular disease), and initial immunosuppressive treatment (Table 1). Transplant variables were cold ischemia time and delayed graft function (DGF)—defined as the need for dialysis within the first week after KT. The final model was chosen using the Akaike Information Criterion,17 which assumes that the lower the values, the better the model.
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TABLE 1.: Baseline characteristics of the initial cohort of patients ≥ 60 y on dialysis placed on the waiting list and the subcohorts of patients who received transplantation from a donor aged 60–79 y and ≥80 y
Comparison Between Recipients and Patients Who Remained on Dialysis
To assess patient survival benefit from KT using kidneys from very elderly deceased donors, we studied 2585 patients ≥60 years old who started RRT, and then we stratified the results for donors between 60 and 79 years and donors ≥80 years. Patient survival was analyzed as the time from first RRT to death or the end of the study period, censoring data at the time of transplantation of those patients who received a KT from a donor younger than 60 years or a dual KT. A time-dependent, nonproportional hazard analysis was used, taking into account that all patients might switch from the dialysis group to the transplantation group during follow-up.
To estimate a model for mortality rates that includes the long- and short-term effect of switching from dialysis to transplant, we used a multiple step function to model the transient risk of transplant. Thus, we used a time-dependent hazard ratio (HR) with steps at several cut points in the Cox model.18
The analysis was performed for the intention to treat; patients were not dropped from the analysis if they were removed from the waiting list or if transplantation failed. We calculated relative risk of death, with the adjustment for the time spent on dialysis.18 The analyses were also adjusted for age at the time of RRT initiation, sex, period of time (before or after y 2000), primary renal disease, having any cardiovascular comorbidity, and having chronic respiratory disease.
Assessing Benefit Limit of Transplantation
We also aimed to determine which elderly patients would not benefit from receiving aged kidneys, so we investigated which factors influenced survival among older KT candidates on dialysis. To increase the power of the sample, the 1212 KT recipients older than 60 years who received a KT from a donor ≥60 years were studied together. We explored whether the benefit of transplantation changed according to different recipients’ characteristics, calculating the interaction between all aforementioned potential mortality risk factors and the KT treatment group.
We also analyzed which factors could be related to better or worse outcomes in both graft and patient survival.
The statistical analysis was carried out by means of the STATA version 13 software.
RESULTS
Baseline Characteristics
Table 1 shows the baseline characteristics of the initial waitlisted cohort and the subcohorts of patients who received a KT during the study period. We found differences between the 2 recipient subcohorts. Donors ≥80 years old were more frequently female candidates. KT recipients from those donors were older (mean age 71.8 ± 4.2 y), more frequently male patients, and presented higher rates of comorbidities, such as chronic respiratory problems or cardiovascular disease. Most of them received the KT in the second period, with higher percentage of sensitized patients and broad thymoglobulin and tacrolimus use. There were no differences in DGF.
Table S1 (SDC, https://links.lww.com/TP/B732) details the causes of discard of 185 organs from donors ≥80 years in 2000 to 2014. The main cause of not considering these organs for transplantation was macroscopic (39%) and microscopic (24.8%) alterations. Donor age was 80 years old (n = 42, 22.9%), 81 (n = 41, 22.9%), 82 (n = 34, 19%), 83 (n = 20, 11.2%), 84 (n = 15, 8.4%), 85 (n = 9, 5%), 86 (n = 7, 3.9%), 87 (n = 6, 3.3%), 88 (n = 3, 1.7%), 89 (n = 2, 1.1%), and 90 years old (n = 1, 0.6%), respectively. Donor mean age was 82.3 years, and 57.5% of them were female candidates.
Analysis of Transplant Outcomes Using Kidneys From Donors ≥80 Years
One- and 5-year graft survival were significantly poorer in KT recipients from extremely elderly donors compared to younger ones (86% and 64% versus 93% and 83%, respectively; P = 0.01). However, we did not find a higher risk of death with functioning graft among the 2 groups of recipients, with 1- and 5-year rates of death with functioning graft of 7% and 21% versus 7% and 22.9%, respectively (P = 0.383). The competing risk regression analysis after adjusting for potential confounders showed that kidneys from donors ≥80 years conferred a marginally increased adjusted risk of graft loss (HR = 1.55; 95% confidence interval [CI] 1.00-2.38; P = 0.048) (Table 2). Lower graft survival was associated with DGF and absence of tacrolimus use as the main immunosuppressive drug given during the first 6 weeks after transplantation. On the contrary, patient survival with functioning graft was associated with advanced recipient age, diabetes as a primary renal disease, and donor gender. Donor age did not impact patient survival (HR = 0.75; 95% CI, 0.48-1.15; P = 0.188) (Table 2).
TABLE 2.: Risk factors for graft loss and patient death with functioning graft among kidney transplant recipients
To assess which organs could succeed and which ones would fail, as well as which recipients could have the potential benefit from these organs and which do not, we compared recipient characteristics from KT coming from donors ≥80 years according to the status at 1 year of follow-up (graft loss, patient death, or kidney still functioning) (Table S2, SDC, https://links.lww.com/TP/B732) and at the end of the observation (Table S3, SDC, https://links.lww.com/TP/B732). We found that recent KTs were still functioning, and immunosuppression based on tacrolimus and basiliximab was also protective.
Comparison Between Patients Who Underwent Transplantation From a Donor Between 60 and 79 Years, Donors ≥80 Years, and Patients Who Remained on Dialysis
Within the group of patients who remained on dialysis, 634 deaths were observed versus 578 in the transplant group (541 were recipients from donors between 60 and 79 y and 37 from donors ≥80 y). The adjusted analysis showed that the survival benefit of receiving a KT from a donor 60 to 79 years was significant 12 months after transplantation in all patient subgroups, regardless of age or comorbidities, with a global HR of 0.50 (CI, 0.44-0.58; P = 0.023, Table 3). When we analyzed this benefit with very old donors (≥80 y), the overall reduction in mortality was 85% (HR = 0.54; 95% CI, 0.38-0.77; P = 0.001) (Table 3).
TABLE 3.: Relative risk of death at 12 mo after kidney transplantation in 2 donor age groups (60–79 y and ≥80 y), compared to remaining on dialysis on the waiting list
Assessing Benefit Limit of Transplantation in Recipients Over 60 Years
The relative risk of death among the 1212 KT recipients ≥60 years compared with patients on dialysis waiting for transplantation is shown in Figure 1. There was an interaction effect between KT survival benefit and time after transplantation. The mortality risk was significantly higher in the transplant group during the first 30 days after transplantation (HR = 2.78; 95% CI, 1.66 to 3.65; P = 0.001), followed by an exponential decay in the long-term, equaling the risk at day 270 and reaching significant benefit 12 months after transplantation (HR = 0.52; 95% CI, 0.00-0.45; P = 0.001).
FIGURE 1.: Relative risk of death among 1212 recipients ≥60 y old with a first kidney transplant from a donor ≥60 y compared with those patients who remained on dialysis waitlisted. The reference group included 2585 patients ≥60 y who started renal replacement therapy (RRT) (relative risk, 1.0). The study group included those who received a transplant from a donor ≥60 y (n = 1212). Patients in both groups had equal lengths of follow-up since initiating RRT. Model was adjusted for age at the beginning of RRT, recipient gender, diabetes as primary renal disease, the presence of any cardiovascular comorbidity, and the period of time when patient received the transplant.
Considering all interaction effects between mortality risk factors and KT, we found that only the recipient with diabetic nephropathy was significant. HR at first year after transplantation in recipients with diabetic nephropathy compared with recipients without diabetic nephropathy was 1.43 (HR = 1.43; 95% CI, 1.05-1.94; P = 0.023) (Table 4). Thus, the benefit of KT in diabetic recipients was attenuated.
TABLE 4.: Adjusted hazard ratio of mortality for all waitlist candidates ≥60 y
Survival benefit of KT from 12 months after KT was also lost gradually as the patient aged but not significantly. We quantified the interaction effect between patient age and KT with a 2% increase in risk of death per year of life in recipients, reaching risk of death for those ≥70 years 25% higher (HR = 1.25; 95% CI, 0.94-1.67; P = 0.119) (Table 4). The profile of lower patient survival was an old male who started dialysis before 2001 and had diabetes mellitus or any cardiovascular comorbidity. In contrast, the highest benefit in survival was conferred by receiving a KT.
DISCUSSION
The present study describes the outcomes using kidneys from the largest cohort of donors ≥80 years old ever reported in the literature. We focused our analysis on elderly recipients (>60 y), the most fragile population, but at the same time the one who most frequently receives these extremely elderly kidneys. Graft survival considering patient death with functioning graft as a competing risk was acceptable (64% at 5 y), although significantly lower compared with KT from younger donors 60 to 79 years old. Despite the fact that advanced donor age is detrimental for graft survival, KT from these extremely old donors still confers a very significant reduction in mortality compared to dialysis. Survival benefit of KT from donors ≥60 years to recipients ≥60 years begins 270 days after transplantation and is clearly significant beyond the first year.
Extremely old donors are not usually considered for transplantation in many countries.15 Very recently, Messina et al reported outcomes with 38 kidneys obtained from octogenarian donors, of which 16 were allocated as single KT and 22 as dual KT, making 27 recipients in total.19 Dual KT has proven a marginal benefit regarding graft survival compared to single KT. Indeed, we have reviewed the issue very recently20 and found the same conclusion. Our approach, however, is not based on graft function but patient survival. We believe that the benefit from dual KT does not justify the use of 2 kidneys in 1 recipient, as we are presenting precisely the opposite: you can use 1 kidney from a donor ≥80 years and, even though, you can get the survival benefit. We should not probably waste 1 kidney to get more GFR in 1 recipient whose life expectancy is not longer than graft survival. The practice of dual KT has been progressively abandoned as we allocate 1 kidney per recipient.14,20
To our knowledge, this is the largest cohort of donors ≥80 years old described so far. Most of these KTs were performed after the year 2000 and came predominantly from female donors. Recipients who received kidneys from these donors were elderly, and more than one-third of them had cardiovascular comorbidities. They were also more sensitized, although this finding is probably related to the change in recent years from classical PRA to calculate PRA based on solid phase assays.21 Summarizing, they constituted a cohort of less healthy KT recipients than previously reported.13
Although expanded criteria donors have been proved to provide shorter graft survival than the standard ones, donor age has been less commonly related to poorer patient survival.7 We found that kidneys from donors ≥80 years old conferred a higher risk of graft loss than those from donors 60 to 79 years, but only recipient age and diabetes mellitus were related to patient survival with functioning graft. Five-year patient and graft survival were even higher than previously reported in elderly recipients receiving kidneys from very old donors.22-24 More importantly, when we compared those patients who received a kidney from donors ≥80 years with those who remained on dialysis, we found a global benefit in survival, even in comorbid patients. This is consistent with previous reports from our group and others,3-5 although it might be slightly different with kidneys that come from donors after circulatory death.9
The importance of our study lies in assessing the current limits in KT. We aimed to determine which elderly patients (≥60 y) would not benefit from receiving those aged kidneys (≥60 y). First, this benefit takes time to be significant. Equal risk of mortality with patients who remained on dialysis is achieved by day 270, and the benefit is significant beyond 1 year after transplantation. This implies a very careful selection of the recipients who might potentially obtain the benefit, that is, those who fulfill the characteristics to overcome the first month after transplantation, when the risk is highest. Second, the benefit loses power as the recipient ages, although the interaction between age and transplantation is not significant. Recipients with diabetes mellitus had a higher risk of mortality compared to those with other ESRD causes, thus attenuating the benefit of KT in diabetic recipients. In a multivariable model for mortality risk among KT candidates, male gender, age, diabetes a primary renal disease, cardiovascular comorbidities, and RRT before year 2001 conferred the risk for mortality. The highest survival benefit was proportioned by KT. On the contrary, we analyzed those recipients who received a kidney from a donor ≥80 years according to their final status (still functioning graft, graft loss, or patient death). We found that more recent transplants, in which current immunosuppression (basiliximab and tacrolimus) was used, were at higher percentage of being still functioning at the end of the study period.
Our main limitation is the lack of more detailed data on the donors and discarded kidneys to help the clinicians to make conclusions on the clinical process. After retrieval, main discard causes were expected, namely macroscopic and microscopic negative features (Table S1, SDC, https://links.lww.com/TP/B732). More detailed characteristics are lacking. In Catalonia, grafts from old recipients are considered to be eligible if they fit criteria regarding donor’s comorbidities, donor’s kidney function, graft macroscopic aspect, and microscopic features assessed by graft biopsy. Once the clinician has all the information, the allocation is based on each center’s criteria as each center manages its own kidney transplant waiting list. The nephrologist and surgeon decide together, taking into account the agreed center criteria, quite uniform in all 6 Catalan centers but without rigid rules or systematic allocation. The biopsy findings have been used during the study period, but criteria have been expanded during the last years when evidence in the literature shows that the isolated value of the biopsy findings is limited. Remuzzi score25,26 has been used by some units for different periods, but there are not uniform criteria. Old-for-old policy is the rule, but other aspects are considered, such as size equivalence among donor and recipient or recipient comorbidities. There is not a systematic allocation based on these characteristics, as there are some aspects that are impossible to measure and quantify. Despite that, we present the largest study with donors ≥80 years that shows a survival benefit compared to maintaining the recipient on dialysis waiting for a better kidney to come. Although we do not have the definitive key to clarify which are the kidneys we can use or not, we demonstrated that these kidneys are suitable to be used, under diverse protocols or conditions. Our study does not answer all the potential questions and doubts but expands the limited experience with such extremely old kidney grafts. In the future, we probably will be able to analyze which factors are the important to be considered for the acceptance of the organ.
Another limitation is that the number of patients receiving extremely old kidneys is relatively small compared with the overall KT cohort, and the results need to be confirmed and extended with a larger cohort in the future. The retrospective nature of our analyses precludes any meaningful prospective strategy to select kidneys and recipients. Therefore, the landmark questions on selecting the appropriate old kidneys and the ideal old recipients to obtain successful outcomes remain to be elucidated with prospective studies. Finally, we were unable to assess quality of life, which may constitute a more crucial factor than life years gained in making decisions on using an old kidney or remaining on dialysis in the case of each particular patient.
In conclusion, our study shows that kidneys from extremely old donors may be eligible for transplantation in old recipients, providing a benefit in survival compared to remaining on dialysis.
ACKNOWLEDGMENTS
The authors thank all the staff working at the Catalan Renal Registry and all the health professionals involved in data managing in the nephrology and kidney transplantation units in Catalonia.
The Follow-up Committee of the Catalan Renal Registry includes the following members: Alberto Martínez-Castelao, Hospital Universitari de Bellvitge, Hospitalet; Maribel Troya, Hospital Germans Trias i Pujol, Badalona; Aleix Cases, Hospital Clínic i Provincial, Barcelona; Dr Jordi Calabia, Hospital Dr Josep Trueta, Girona; Higinio Cao, Hospital del Mar, Barcelona; Alfons Segarra, Hospital Arnau de Vilanova, Lleida; Alberto Martínez-Vea, Hospital Joan XXIII, Tarragona; Salvador Gil-Vernet, Hospital Universitari de Bellvitge, Hospitalet; Eugenia Espinel, Hospital Vall d’Hebron, Barcelona; Enrique Lara, Hospital Materno-Infantil Vall d’Hebron, Barcelona; Joan Manel Díaz, Fundació Puigvert, Barcelona; Emma Arcos, Jordi Comas and Jaume Tort, Registre de malalts renals de Catalunya, Organització Catalana de Trasplantaments.
Our thanks to Fidelma Greaves for English translation and editing.
REFERENCES
1. Wolfe RA, Ashby VB, Milford EL, et al. Comparison of mortality in all patients on dialysis, patients on dialysis awaiting transplantation, and recipients of a first cadaveric transplant. N Engl J Med. 1999; 341:1725–1730
2. Ojo AO, Hanson JA, Meier-Kriesche H, et al. Survival in recipients of marginal cadaveric donor kidneys compared with other recipients and wait-listed transplant candidates. J Am Soc Nephrol. 2001; 12:589–597
3. Lloveras J, Arcos E, Comas J, et al. A paired survival analysis comparing hemodialysis and kidney transplantation from deceased elderly donors older than 65 years. Transplantation. 2015; 99:991–996
4. Pérez-Sáez MJ, Arcos E, Comas J, et al.; Catalan Renal Registry Committee. Survival benefit from kidney transplantation using kidneys from deceased donors aged ≥75 years: a time-dependent analysis. Am J Transplant. 2016; 16:2724–2733
5. Gill JS, Lan J, Dong J, et al. The survival benefit of kidney transplantation in obese patients. Am J Transplant. 2013; 13:2083–2090
6. ERA-EDTA Registry:
ERA-EDTA Registry Annual Report 2015.
Academic Medical Center, Department of Medical Informatics, Amsterdam, the Netherlands, 2017. Available at
https://www.era-edta-reg.org/files/annualreports/pdf/AnnRep2015.pdf. Accessed September 1, 2018
7. Pérez-Sáez MJ, Montero N, Redondo-Pachón D, et al. Strategies for an expanded use of kidneys from elderly donors. Transplantation. 2017; 101:727–745
8. Catalan Renal RegistryStatistical Report 2015. 2015. Barcelona, Spain: Catalan Transplant Organization, Health Department. Available at
http://trasplantaments.gencat.cat/web/.content/minisite/trasplantament/registres_activitat/registre_de_malalts_renals/arxius/Informe-2015-FINAL.pdf. Accessed June 30, 2017
9. Kasiske BL, Cangro CB, Hariharan S, et al.; American Society of Transplantation. The evaluation of renal transplantation candidates: clinical practice guidelines. Am J Transplant. 2001; 1(Suppl 2):3–95
10. Knoll G, Cockfield S, Blydt-Hansen T, et al.; Kidney Transplant Working Group of the Canadian Society of Transplantation. Canadian society of transplantation: consensus guidelines on eligibility for kidney transplantation. CMAJ. 2005; 173:S1–25
11. The Renal AssociationClinical Practice Guidelines. The Renal Association website. Available at
http://www.renal.org/pages/pages/guidelines/current/transplantation.php. Accessed February 26, 2019
12. Peters-Sengers H, Berger SP, Heemskerk MB, et al. Stretching the limits of renal transplantation in elderly recipients of grafts from elderly deceased donors. J Am Soc Nephrol. 2017; 28:621–631
13. Lønning K, Midtvedt K, Leivestad T, et al. Are octogenarians with end-stage renal disease candidates for renal transplantation? Transplantation. 2016; 100:2705–2709
14. . Memorias de actividad y donación en trasplantes, año 2017. Available at
http://www.ont.es/infesp/Memorias/Memoria%20Donaci%C3%B3n%202017.pdf. Accessed September 1, 2018
15. Unit Network for Organ SharingAnnual Report, 2015. UNOS website. Available at
https://www.unos.org/about/annual-report/. Accessed June 30, 2017
16. Klein JP, Moeschberger MV. Survival Analysis: Techniques for Censored and Truncated Data: Statistics for Biology and Health. 2003, 2nd ed. New York, NY: Springer
17. Burnham KP, Anderson DR. Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach. 2002, 2nd ed. New York, NY: Springer-Verlag
18. Mauger EA, Wolfe RA, Port FK. Transient effects in the cox proportional hazards regression model. Stat Med. 1995; 14:1553–1565
19. Messina M, Diena D, Dellepiane S, et al. Long-term outcomes and discard rate of kidneys by decade of extended criteria donor age. Clin J Am Soc Nephrol. 2017; 12:323–331
20. Montero N, Redondo-Pachón D, Pérez-Sáez MJ, et al. Dual kidney transplantation as a strategy to use expanded criteria donors: a systematic review. Transpl Int. 2018; 31:838–860
21. Cecka JM. Calculated PRA (CPRA): the new measure of sensitization for transplant candidates. Am J Transplant. 2010; 10:26–29
22. Al-Shraideh Y, Farooq U, Farney AC, et al. Influence of recipient age on deceased donor kidney transplant outcomes in the expanded criteria donor era. Clin Transplant. 2014; 28:1372–1382
23. Mezrich JD, Pirsch JD, Fernandez LA, et al. Differential outcomes of expanded-criteria donor renal allografts according to recipient age. Clin J Am Soc Nephrol. 2012; 7:1163–1171
24. Frei U, Noeldeke J, Machold-Fabrizii V, et al. Prospective age-matching in elderly kidney transplant recipients–a 5-year analysis of the eurotransplant senior program. Am J Transplant. 2008; 8:50–57
25. Remuzzi G, Cravedi P, Perna A, et al.; Dual Kidney Transplant Group. Long-term outcome of renal transplantation from older donors. N Engl J Med. 2006; 354:343–352
26. Ruggenenti P, Silvestre C, Boschiero L, et al. Long-term outcome of renal transplantation from octogenarian donors: a multicenter controlled study. Am J Transplant. 2017; 17:3159–3171
