A critical assessment on kidney allocation systems

Beyond Immunity: Challenges in Kidney Retransplantation Among Persons Living With HIV

INTRODUCTION

While superb outcomes have been observed in the HIV-positive (HIV+) population, graft failure and subsequent need for kidney retransplantation (re-KT) remain a concern. This study aims to investigate the difference in success rates of re-KT allograft survival in the HIV+ versus HIV-negative (HIV-) population in the current era of transplantation (2014-2022).

METHODS

Data was collected from the Organ Procurement and Transplantation Network on all kidney transplant donors and recipients who had their first re-KT between 2014 and 2022. Allograft survival was assessed using Kaplan-Meier analysis with a log-rank test, while risk factors for graft loss were assessed using Cox proportional hazards with statistical significance set to P = 0.05.

RESULTS

HIV+ recipients were significantly more likely to be Black (P < 0.001), have an HLA mismatch >3 (P = 0.018), delayed graft function (P = 0.023), and graft loss from primary nonfunction (P < 0.001). Their HIV- counterparts were more likely to be White (P < 0.001) and Hispanic (<0.001), lose their graft from acute rejection (P = 0.044), and have a living donor (P = 0.001). Being HIV+ was associated with a 1.68-fold increased risk of graft loss, an HLA mismatch >3 held a 1.18-fold increase, experiencing delayed graft function held a 1.89-fold increase, and having diabetes was associated with a 1.16-fold increased risk. Living donor kidneys were associated with a 15.8% decrease in risk for graft failure. Kaplan-Meier curves showed a significantly lower duration of kidney allograft survival in the HIV+ community (P = 0.02).

CONCLUSIONS

Disproportional graft failure and inadequate HLA mismatching persist within the HIV+ Re-KT community. Stronger organ matching and new approaches for desensitizing retransplant candidates are vital.

Equity matrix for kidney transplant allocation

There is a general agreement that the distribution of kidneys for transplantation should balance utility criteria with justice. Moreover, a kidney allocation system must be based on transparent policies and seen as an ongoing process. This study aims to present an allocation system grounded on an equity matrix that balances the criteria of utility and justice. Synthetic data for a waiting list with 2000 transplant candidates and a pool of 280 donors were generated. A color priority system, the Eurotransplant (ET) kidney allocation system, and the proposed Equity Matrix (EQM) allocation system were compared after 1000 iterations of kidney allocations. Distributions of variables like the age difference, Human Leukocyte Antigens (HLA) mismatches (mmHLA), recipients' time on dialysis, cPRA, and a transplant score obtained by different allocation models were compared graphically and with Cohen's d effect size. For the analyzed variables, when we compare only the selected recipients from ET with the selected recipients from the EQM neutral model, we can conclude that the former model selects more hypersensitized recipients, a higher number of 65+ years' old recipients with 65+ years' old donors and higher number of recipients with 0 mmHLA. While recipients from EQM neutral are slightly older, have a lower age difference with their donors, have a lower number of mmHLA, are less likely to have 6 mmHLA with their donors, and have more time on dialysis. The proposed EQM model attempts to provide a simple, transparent, and equitable response to a complex question with results that outperform established practices.

Evolving Trends in Kidney Transplant Outcomes Among Older Adults: A Comparative Analysis Before and During the COVID-19 Pandemic

Background

Advancements in medical technology, healthcare delivery, and organ allocation resulted in improved patient/graft survival for older (age ≥65) kidney transplant (KT) recipients. However, the recent trends in these post-KT outcomes are uncertain in light of the mounting burden of cardiovascular disease, changing kidney allocation policies, heterogeneity in candidates' risk profile, and the coronavirus disease 2019 pandemic. Thus, we examined secular trends in post-KT outcomes among older and younger KT recipients over the last 3 decades.

Methods

We identified 73 078 older and 378 800 younger adult (aged 18-64) recipients using Scientific Registry of Transplant Recipients (1990-2022). KTs were grouped into 6 prepandemic eras and 1 postpandemic-onset era. Kaplan-Meier and Cox proportional hazards models were used to examine temporal trends in post-KT mortality and death-censored graft failure.

Results

From 1990 to 2022, a 19-fold increase in the proportion of older KT recipients was observed compared to a 2-fold increase in younger adults despite a slight decline in the absolute number of older recipients in 2020. The mortality risk for older recipients between 2015 and March 14, 2020, was 39% (adjusted hazard ratio [aHR] = 0.61, 95% confidence interval [CI], 0.50-0.75) lower compared to 1990-1994, whereas that for younger adults was 47% lower (aHR = 0.53, 95% CI, 0.48-0.59). However, mortality risk during the pandemic was 25% lower (aHR = 0.75, 95% CI, 0.61-0.93) in older adults and 37% lower in younger adults (aHR = 0.63, 95% CI, 0.56-0.70) relative to 1990-1994. For both populations, the risk of graft failure declined over time and was unaffected during the pandemic relative to the preceding period.

Conclusions

The steady improvements in 5-y mortality and graft survival were disrupted during the pandemic, particularly among older adults. Specifically, mortality among older adults reflected rates seen 20 y prior.

Kidney transplant in the next decade: Strategies, challenges and vision of the future

Although the results of kidney transplantation (KT) have improved substantially in recent years, a chronic and inexorable loss of grafts mainly due to the death of the patient and chronic dysfunction of the KT, continues to be observed. The objectives, thus, to optimize this situation in the next decade are fundamentally focused on minimizing the rate of kidney graft loss, improving patient survival, increasing the rate of organ procurement and its distribution, promoting research and training in health professionals and the development of scientific registries providing clinical and reliable information that allow us to optimize our clinical practice in the field of KT. With this perspective, this review will deep into: (1) strategies to avoid chronic dysfunction and graft loss in the medium and long term; (2) to prolong patient survival; (3) strategies to increase the donation, maintenance and allocation of organs; (4) promote clinical and basic research and training activity in KT; and (5) the analysis of the results in KT by optimizing and merging scientific registries.

Evaluation of Kidney Donor Risk Index/Kidney Donor Profile Index as Predictor Tools of Deceased-Donor Kidney Transplant Outcomes in a Greek Cohort

The Kidney Donor Risk Index (KDRI) and Kidney Donor Profile Index (KDPI) have been developed to assess deceased-donor graft quality, although validation of their utility outside the USA remains limited. This single-center retrospective cohort study evaluated the ability of KDRI and KDPI to predict transplant outcomes in a Greek cohort. The efficacy of KDRI, KDPI, and donor's age in predicting death-censored graft failure was primarily assessed. Overall, 394 donors and 456 recipients were included. Death-censored graft survival was significantly worse with increasing KDRI (hazard ratio-HR: 2.21, 95% confidence intervals-CI: 1.16-4.22), KDPI (HR: 1.01, 95% CI: 1.00-1.02), and donor's age (HR: 1.03, 95% CI: 1.00-1.05). The unadjusted discriminative ability was similar for KDPI (C-statistic: 0.54) and donor's age (C-statistic: 0.52). The KDPI threshold of 85 was not predictive of graft failure (p-value: 0.19). Higher KDPI was linked to delayed graft function and worse kidney function, but not among expanded-criteria donor transplantations. No significant association was found between KDRI, KDPI, and patient survival. In conclusion, increasing KDRI and KDPI are linked to worse graft function, although their ability to discriminate long-term graft failure remains limited.

Is Exclusion of Coronary Artery Disease in the Kidney Allocation System Preventing Optimal Longevity Matching?

BACKGROUND

Coronary artery disease (CAD) in a kidney transplant candidate is an important predictor of posttransplant mortality. It is not known how the exclusion of CAD in the kidney allocation system has impacted its goal of longevity matching.

METHODS

This is an observational study on adult deceased donor kidney transplant alone recipients between December 4, 2014, and December 31, 2018, with Medicare fee for service (FFS) insurance. Patients were categorized on the basis of Kidney Donor Profile Index (KDPI), Estimated Posttransplant Survival (EPTS), and CAD. Outcomes studied were mortality, death with a functioning graft, overall graft loss, and death-censored graft loss.

RESULTS

Among 21 151 patients with Medicare FFS coverage for >1 y before transplant, there were 2869 and 18 282 patients with and without CAD, respectively. On Kaplan-Meier analysis, there was higher risk of mortality, death with a functioning graft, overall graft loss, and death-censored graft loss with CAD ( P < 0.05 for all). Mortality was higher for CAD group within each category of KDPI and among patients with Estimated Posttransplant Survival 0% to 20% receiving kidneys with KDPI <20% ( P < 0.001 for all). On Cox multivariate analysis, the hazard ratios (HRs) of mortality and graft loss were higher with CAD diagnosis without intervention (HR 1.38 [1.25-1.52] and 1.29 [1.18-1.4]), CAD with stents (HR 2.76 [1.68-4.53] and 2.36 [1.46-3.81]), and CAD with bypass surgery (HR 1.56 [1.29-1.89] and 1.39 [1.17-1.65]). Posttransplant CAD events were higher in patients with preexisting CAD ( P < 0.001).

CONCLUSIONS

The exclusion of a candidate's history of CAD in the kidney allocation system adversely impacts its goal of optimal longevity matching.

Kidney Organ Allocation System: How to Be Fair

Transplantation is a life-saving medical intervention that unfortunately is constrained by scarcity of available organs. An ideal system for allocating organs should seek to achieve the greatest good for the greatest number of people. It also must be fair and not disadvantage certain populations. However, policies aimed at reducing disparities also must be balanced with considerations of utility (graft outcomes), cost, efficiency, and any adverse effects on organ utilization. Here, we discuss the ethical challenges of creating a fair and equitable organ allocation system, focusing on the principles governing deceased donor kidney transplant waitlists around the world. The kidney organ allocation systems in the United States, Australia, and Hong Kong are used as illustrations.

Kidney Allocation Policy: Past, Present, and Future

Despite an increase in the number of kidney transplants performed annually, there remain more than 90,000 individuals awaiting transplantation in the United States. As kidney transplantation has evolved, so has kidney allocation policies. The Kidney Allocation System, which was introduced in 2014, made significant strides to improve utility and equity, but regional and geographic disparities remain. Further modifications eliminating donor service areas have been introduced. Moving forward, systems involving continuous distribution and artificial intelligence may provide further advancement toward an ideal allocation system.

Return to work after deceased donor kidney transplant under the kidney allocation system

BACKGROUND

The Kidney Allocation System (KAS) includes a scoring system to match transplant candidate life expectancy with expected longevity of the donor kidney, and a backdating policy that gives waitlist time credit to patients waitlisted after starting dialysis treatment (post-dialysis). We estimated the effect of the KAS on employment among patient subgroups targeted by the policy.

METHODS

We used a sample selection model to compare employment after transplant before and after KAS implementation among patients on the kidney-only transplant waitlist between December 4, 2011 and December 31, 2017.

RESULTS

Post-dialysis transplant recipients aged 18-49 were significantly more likely to be employed 1-year post transplant in the post-KAS era compared to the pre-KAS era. Transplant recipients aged 35-64 with no dialysis treatment were significantly less likely to be employed 1 year after transplant in the post-KAS era compared to the pre-KAS era.

CONCLUSIONS

This study provides the first assessment of employment after DDKT under the KAS and provides important information about both the methods used to measure employment after transplant and the outcome under the KAS. Changes in employment after DDKT among various patient subgroups have important implications for assessing long-term patient and societal effects of the KAS and organ allocation policy.

Use of expanded-criteria donors and > 85 KDPI kidneys for pediatric kidney transplantation in the United States

Pediatric kidney transplant outcomes associated with expanded-criteria donors (ECD) and high Kidney Donor Profile Index (KDPI) kidneys are unknown. We reviewed the Scientific Registry of Transplant Recipients data from 1987-2017 to identify 96 ECD and 92 > 85 KDPI kidney recipients (<18 years). Using propensity scores, we created comparison groups of 375 non-ECD and 357 ≤ 85 KDPI recipients for comparisons with ECD and > 85 KDPI transplants, respectively. We used Cox regression for patient/graft survival and sequential Cox approach for survival benefit of ECD and > 85 KDPI transplantationvs remaining on the waitlist. After adjustment, ECD recipients were at significantly increased risk of graft failure (adjusted hazard ratio [aHR] = 1.6; P = .001) but not of mortality (aHR = 1.33; P = .15) compared with non-ECD recipients. We observed no survival benefit of ECD transplants vs remaining on the waitlist (aHR = 1.05; P = .83). We found no significant difference in graft failure (aHR = 1.27; P = .12) and mortality (aHR = 1.41; P = .13) risks between > 85 KDPI and ≤ 85 KDPI recipients. However, > 85 KDPI transplants were associated with a survival benefit vs remaining on the waitlist (aHR = 0.41; P = .01). ECD transplantation in children is associated with a high graft loss risk and no survival benefit, whereas > 85 KDPI transplantation is associated with a survival benefit for children vs remaining on the waitlist.

Deceased donor kidney allocation: an economic evaluation of contemporary longevity matching practices

BACKGROUND

Matching survival of a donor kidney with that of the recipient (longevity matching), is used in some kidney allocation systems to maximize graft-life years. It is not part of the allocation algorithm for Australia. Given the growing evidence of survival benefit due to longevity matching based allocation algorithms, development of a similar kidney allocation system for Australia is currently underway. The aim of this research is to estimate the impact that changes to costs and health outcomes arising from 'longevity matching' on the Australian healthcare system.

METHODS

A decision analytic model to estimate cost-effectiveness was developed using a Markov process. Four plausible competing allocation options were compared to the current kidney allocation practice. Models were simulated in one-year cycles for a 20-year time horizon, with transitions through distinct health states relevant to the kidney recipient. Willingness to pay was considered as AUD 28000.

RESULTS

Base case analysis indicated that allocating the worst 20% of Kidney Donor Risk Index (KDRI) donor kidneys to the worst 20% of estimated post-transplant survival (EPTS) recipients (option 2) and allocating the oldest 25% of donor kidneys to the oldest 25% of recipients are both cost saving and more effective compared to the current Australian allocation practice. Option 2, returned the lowest costs, greatest health benefits and largest gain to net monetary benefits (NMB). Allocating the best 20% of KDRI donor kidneys to the best 20% of EPTS recipients had the lowest expected incremental NMB.

CONCLUSION

Of the four longevity-based kidney allocation practices considered, transplanting the lowest quality kidneys to the worst kidney recipients (option 2), was estimated to return the best value for money for the Australian health system.

A Virtual Crossmatch-based Strategy Facilitates Sharing of Deceased Donor Kidneys for Highly Sensitized Recipients

BACKGROUND

It is estimated that 19.2% of kidneys exported for candidates with >98% calculated panel reactive antibodies are transplanted into unintended recipients, most commonly due to positive physical crossmatch (PXM). We describe the application of a virtual crossmatch (VXM) that has resulted in a very low rate of transplantation into unintended recipients.

METHODS

We performed a retrospective review of kidneys imported to our center to assess the reasons driving late reallocation based on the type of pretransplant crossmatch used for the intended recipient.

RESULTS

From December 2014 to October 2017, 254 kidneys were imported based on our assessment of a VXM. Of these, 215 (84.6%) were transplanted without a pretransplant PXM. The remaining 39 (15.4%) recipients required a PXM on admission using a new sample because they did not have an HLA antibody test within the preceding 3 months or because they had a recent blood transfusion. A total of 93% of the imported kidneys were transplanted into intended recipients. There were 18 late reallocations: 9 (3.5%) due to identification of a new recipient medical problem upon admission, 5 (2%) due to suboptimal organ quality on arrival, and only 4 (1.6%) due to a positive PXM or HLA antibody concern. A total of 42% of the recipients of imported kidneys had a 100% calculated panel reactive antibodies. There were no hyperacute rejections and very infrequent acute rejection in the first year suggesting no evidence for immunologic memory response.

CONCLUSIONS

Seamless sharing is within reach, even when kidneys are shipped long distances for highly sensitized recipients. Late reallocations can be almost entirely avoided with a strategy that relies heavily on VXM.

Kidney transplantation for the primary care provider

Advancement in kidney transplantation has led to prolonged survival in our population with kidney disease. Newer agents of immunosuppression have made this possible with less rejections and lesser opportunistic infections and transplant related deaths. Preventative care like timely vaccines, cancer screenings, aggressive blood pressure, blood sugar, lipid control, timely referral to consultants is required in these patient population to provide quality care and to prolong their survival. Primary care physicians are the best advocate for our transplant populations. To care for these complex transplant patients, it is vital for primary care physicians to be familiar with the overall approach on our patients.

Prospective Validation of Prediction Model for Kidney Discard

BACKGROUND

Many kidneys are discarded every year, with 3631 kidneys discarded in 2016 alone. Identifying kidneys at high risk of discard could facilitate "rescue" allocation to centers more likely to transplant them. The Probability of Delay or Discard (PODD) model was developed to identify marginal kidneys at risk of discard or delayed allocation beyond 36 hours of cold ischemia time. However, PODD has not been prospectively validated, and patterns of discard may have changed after policy changes such as the introduction of Kidney Donor Profile Index and implementation of the Kidney Allocation System (KAS).

METHODS

We prospectively validated the PODD model using Scientific Registry of Transplant Recipients data in the KAS era (January 1, 2015, to March 1, 2018). C statistic was calculated to assess accuracy in predicting kidney discard. We assessed clustering in centers' utilization of kidneys with PODD >0.6 ("high-PODD") using Gini coefficients. Using match run data from January 1, 2015, to December 31, 2016, we examined distribution of these high-PODD kidneys offered to centers that never accepted a high-PODD kidney.

RESULTS

The PODD model predicted discard accurately under KAS (C-statistic, 0.87). Compared with utilization of low-PODD kidneys (Gini coefficient = 0.41), utilization of high-PODD kidneys was clustered more tightly among a few centers (Gini coefficient, 0.84 with >60% of centers never transplanted a high-PODD kidneys). In total, 11684 offers (35.0% of all high-PODD offers) were made to centers that never accepted a high-PODD kidney.

CONCLUSIONS

Prioritizing allocation of high-PODD kidneys to centers that are more likely to transplant them might help reduce kidney discard.

United Network for Organ Sharing Rule Changes and Their Effects on Kidney and Liver Transplant Outcomes

OBJECTIVES

Recent national organ distribution rule changes could have implications on distance between donor and recipient hospitals and cold ischemia time. With cold ischemia time being an unavoidable detriment to organ quality, any strategies that minimize it should maximize organ quality. This study evaluated the significance of the kidney allocation system and the Share 35 rule changes on kidney and liver transplant outcomes.

MATERIALS AND METHODS

This retrospective study included deceased liver and kidney donor and their recipient data from the Organ Procurement and Transplantation Network. Variables were analyzed using propensity score matching and Cox hazards model distance (from donor hospital to organ recovery center), and effects on survival outcomes of trans-planted livers and kidneys in the context of the recent rule changes were analyzed.

RESULTS

Transplanted organs have significantly better outcomes when the distance is 0 miles versus median distances for locally transported organs of 18 and 22 miles for kidney and liver, respectively. Cold ischemia time, when corrected, accounts for this finding, thus suggesting that cold ischemia time is the factor most responsible for viability of a transplanted organ. This significance remains evident for liver transplants even after the Share 35 rule change but not for kidney transplants following the December 2014 kidney allocation system change.

CONCLUSIONS

Liver transplants showed a higher risk of lower viability with travel, and the Share 35 rule did not appear to change this result. Kidney transplant outcomes appear to have improved after the kidney allocation system change. Potential strategies for minimizing cold ischemia time and improving outcomes include more free-standing organ recovery centers in centralized locations.

Burden of excess mortality after implementation of the new kidney allocation system may be borne disproportionately by middle-aged recipients

Under the new kidney allocation system (KAS), implemented in 2014, the distribution of the best quality donor kidney grafts shifted between age groups, but it is unclear whether this change translates to meaningful differences in post-transplant outcomes. We conducted a retrospective cohort study of 20,345 deceased donor kidney transplant recipients before and 4,605 recipients after implementation of the KAS using data from the United Network of Organ Sharing. Overall, two-year mortality was greater among recipients in the post-KAS era compared with the pre-KAS era (6.31% vs 5.91% respectively, [p = 0.01]), and two-year graft loss was not significantly different between eras (9.95% and 9.65%, respectively [p = 0.13]). In analysis stratified by age group (18-45, 46-55, 56-65, and ≥66 years), relative risk of mortality was 1.48 (95% confidence interval [CI] 1.09-1.98) among recipients 46-55 years old and 1.47 (95% CI 1.18-1.81) among recipients 56-65 years old. Relative risk of all-cause graft loss was 1.43 (95% CI 1.20-1.70) among recipients 56-65 years old. There were no significant differences in relative risk of mortality or graft loss associated with the KAS era among other age groups. After adjustment for recipient characteristics and characteristics of the changing donor pool, relative risk of two-year mortality and graft loss associated with the post-KAS era was attenuated for recipients aged 46-55 and 56-65 years, but remained statistically significant. In this early analysis after implementation of the KAS, there is suggestion that increased risk of mortality and graft loss may be disproportionately borne by middle-aged recipients, which is only partially accounted for by changes in recipient and donor characteristics. These findings signal a need to continue to monitor the effects of the KAS to ensure that allocation practices both maximize utility of the kidney graft pool and respect fairness between age groups.

Impact of the kidney allocation system on young pediatric recipients

The kidney allocation system (KAS) altered pediatric candidate prioritization. We determined KAS's impact on pediatric kidney recipients by examining delayed graft function (DGF) rates from 2010 to 2016. A propensity score-matched pediatric recipients pre- and post-KAS. A semiparametric decomposition analysis estimated the contributions of KAS-related changes in donor characteristics and dialysis time on DGF rate. The unadjusted odds of DGF were 69% higher post-KAS for young (<10 years at listing) recipients (N = 1153, P = .02) but were not significantly increased for older pediatric (10-17 years at listing) recipients (N = 2624, P = .48). Post-KAS, young recipients received significantly fewer pediatric (<18 years) donor kidneys (21% vs 32%, P < .01) and had longer median pretransplant dialysis time (603 vs 435 days, P < .01). After propensity score matching, post-KAS status increased the odds of DGF in young recipients 71% (OR 1.71, 95% CI 1.01-2.46). In decomposition analysis, 24% of the higher DGF rate post-KAS was attributable to donor characteristics and 19% to increased recipient dialysis time. In a confirmatory survival analysis, DGF was associated with a 2.2 times higher risk of graft failure (aHR2.28, 95% CI 1.46-3.54). In conclusion, KAS may lead to worse graft survival outcomes in children. Allocation changes should be considered.

Harnessing Scientific and Technological Advances to Improve Equity in Kidney Allocation Policies

We reported that current assignment of HLA-DQ is a barrier to organ allocation. Here we simulated the impact of incorporating HLA-DQ antigens and antibodies as A/B and αβ allelic variants, respectively, on calculated panel reactive antibody (cPRA) and probability of finding potential compatible donors (PCD). A cohort of 1224 donors and 2075 sensitized candidates was analyzed using HLA-DQαβ allelic (study) versus serologic (current practice) nomenclature. A significant (p < 10^-4 ) decrease in cPRA was observed with higher impact for male versus female, and first transplant versus retransplant (p < 10^-4 ), affecting mostly patients with moderate cPRA (30-80%). Consequently, the number of patients qualifying for 100% cPRA points according to the United Network for Organ Sharing-Kidney Allocation System decreased by 37%. More critically, by using allelic versus serologic nomenclature for HLA-DQ, the number of PCDs for all patients was increased, with male and first-transplant patients showing a higher expansion compared with female and retransplants. Patients of blood group O showed the highest benefit. The goal of reporting unacceptable antigens is to improve accuracy of virtual crossmatching and increase the likelihood of finding immunologically compatible donors. Our simulation provides strong support for the need to re-evaluate the use of allele typing and how HLA-DQ antigens and antibodies are incorporated into allocation policies to ensure equity.