Kidney Allocation System Research Articles

A novel two-stage network data envelopment analysis model for kidney allocation problem under medical and logistical uncertainty: a real case study.

Organ transplantation is one of the most complicated and challenging treatments in healthcare systems. Despite the significant medical advancements, many patients die while waiting for organ transplants because of the noticeable differences between organ supply and demand. In the organ transplantation supply chain, organ allocation is the most significant decision during the organ transplantation procedure, and kidney is the most widely transplanted organ. This research presents a novel method for assessing the efficiency and ranking of qualified organ-patient pairs as decision-making units (DMUs) for kidney allocation problem in the existence of COVID-19 pandemic and uncertain medical and logistical data. To achieve this goal, two-stage network data envelopment analysis (DEA) and credibility-based chance constraint programming (CCP) are utilized to develop a novel two-stage fuzzy network data envelopment analysis (TSFNDEA) method. The main benefits of the developed method can be summarized as follows: considering internal structures in kidney allocation system, investigating both medical and logistical aspects of the problem, the capability of expanding to other network structures, and unique efficiency decomposition under uncertainty. Moreover, in order to evaluate the validity and applicability of the proposed approach, a validation algorithm utilizing a real case study and different confidence levels is used. Finally, the numerical results indicate that the developed approach outperforms the existing kidney allocation system.

Associations Among Circle-Based Kidney Allocation, Center Waiting Time, and Likelihood of Deceased-Donor Kidney Transplantation

The kidney allocation system (KAS250), using circle-based distribution, attempts to address geographic disparities through broader sharing of deceased-donor kidney allografts. This study sought to evaluate the association between KAS250 and likelihood of deceased-donor kidney transplantation (DDKT) among waitlisted candidates, and whether the policy has differentially affected centers with shorter vs. longer waiting time. Retrospective cohort study. & Participants: 160,941 candidates waitlisted at 176 transplant centers between 3/2017-3/2024. KAS250 allocation policy. Rate of DDKT. Multivariable Cox regression, modeling KAS250 as a time-dependent variable. KAS250 was not independently associated with likelihood of DDKT overall (HR=1.01 vs. pre-KAS250, 95% C.I. 0.97-1.04). KAS250's association with likelihood of DDKT varied across centers from HR=0.18 (DDKT less likely after KAS250) to HR=17.12 (DDKT more likely) and varied even among neighboring centers. KAS250 was associated with decreased DDKT at 25.6% and increased DDKT at 18.2% of centers. Centers with previously long median waiting times (57+ months) experienced increased likelihood of DDKT after KAS250 (HR=1.20, 95% C.I. 1.15-1.26), whereas centers with previously short median waiting times (6-24mo.; HR=0.88, 0.84-0.92) experienced decreased likelihood of DDKT. Retrospective study of allocation policy changes, confounded by multiple changes over the study timeframe. Association between KAS250 and DDKT varied across centers. For one-in-four centers, DDKT was less likely after KAS250 relative to pre-KAS250 trends. Candidates at centers with previously long waiting times experienced increased likelihood of DDKT after KAS250. Thus, broader distribution of kidneys may be associated with improved equity in access to DDKT, but additional strategies may be needed to minimize disparities between centers.

Personal Viewpoint: Navigating Challenges in Recipient Selection for End-Chain Kidneys

As a result of the increasing number of transplants being facilitated by kidney paired donation, and newer initiatives such as voucher donation, end-chain kidneys now constitute a considerable proportion of kidney paired donation transplants in the United States. Data on end-chain kidneys are limited. They may be lower in quality compared to non-end chain living donor kidneys. However, they can provide unique opportunities for recipient candidates without living donors. There are no data or algorithms available to guide recipient selection for end-chain kidneys accepted by a transplant center. Considering the ethical principles of utility, justice, and respect for persons that underlie organ allocation, we discuss three potential approaches for recipient selection: 1) adherence to the Kidney Allocation System, 2) utility maximization and 3) priority to high-risk candidates, along with examples from our own center’s experience. Similar considerations are also relevant to selection of recipients for non-directed donor organs, and to out-of-sequence allocation for deceased organ donors. Since end-chain kidneys represent an increasingproportion of kidney paired donation-facilitated living kidney donor transplantation in the United States, and will likely get more medically and surgically complex over time, ongoing research on their utilization and outcomes is needed.

Highly Sensitized Kidney Transplant Outcomes After the 2014 Kidney Allocation System Change.

Introduction: Kidney Allocation System (KAS) was implemented by United Network for Organ Sharing in 2014 to reduce allocation disparities. Research Questions: Outcomes of highly sensitized patients (calculated panel reactive antibody (cPRA) ≥ 97%) before and after KAS were compared to low-risk recipients (cPRA <10%) in the post-KAS era were examined. The impact on racial disparities was determined. Design: This was a retrospective study of national registry data. Two cohorts of adult candidates waitlisted for deceased donor transplantation during 3-year periods before and after KAS were identified. Results: Highly sensitized patients (N = 1238 and 4687) received a deceased donor kidney transplant between January 1, 2011 and December 31, 2013 and between January 1, 2015 and December, 31, 2017. Racial disparity for highly sensitized patients improved, yet remained significant (P < 0.001), with Black patients comprising 40% and 41% of the highly sensitized candidates and 28% and 34% of the recipients pre- and post-KAS. While posttransplant death-censored graft failure for highly sensitized recipients was similar overall, post-KAS was associated with improved graft survival in the first year after transplant (HR 0.56, 95% CI 0.40-0.78). When compared to contemporaneous lowrisk recipients, both death-censored and all-cause graft failure were similar for highly sensitized recipients and was associated with increased risk for death-censored graft failure beyond the first year (HR 1.39, 95% CI 1.11-1.73). Conclusion: The allocation system led to an increase in transplantation in highly sensitized candidates without compromising outcomes. Although KAS has led to more balanced transplant rates between highly sensitized Black and White patients, racial inequalities persist.

Diagnosing the Recent Decrease in Utilization of Deceased Donor Kidneys.

The number of deceased donor kidney transplants has been increasing and is at a record high, yet nonuse of kidneys recovered for transplantation has risen to 25.8% following circular kidney allocation system based on 250-nautical-mile circles implemented on March 15, 2021 (KAS250). Using Scientific Registry of Transplant Recipients data, we studied all deceased donor kidneys recovered for transplant from March 15, 2019, to January 31, 2023. We calculated the association of multiple factors with kidney nonuse, including increasing recovery of kidneys from nonideal donors, delays in offer acceptance observed under KAS250, and impacts of COVID-19. In the 2 y before KAS250, the nonuse rate was 21.2%. Had this rate continued, 2334 more kidneys would have been transplanted through January 2023. We estimated that about 769 of these nonused kidneys (33%) were associated with offer acceptance delays under KAS250; about 994 of these nonused kidneys (43%) were associated with increased prevalence of nonideal donors: donation after circulatory death donors, older donors, and donors with elevated peak serum creatinine; and about 542 of these nonused kidneys (23%) were associated with an otherwise unexplained gradual upward trend in nonuse of recovered kidneys across the pre-KAS250 and KAS250 eras. The overall impact of COVID-19 on the nonuse rate was not significant. The rise in kidney nonuse rate was significantly associated with both increased recovery of nonideal donors, and with KAS250 allocation complexity and delays. Increasing recovery of kidneys from nonideal donors benefits patients because recovering more kidneys increases the number of kidneys available for transplant.

Allocation Rules and Age-Dependent Waiting Times for Kidney Transplantation.

Rigid age limits in the current allocation system for post-mortem donor kidneys in Germany may have problematic effects. The new German national transplantion registry enables data analysis with respect to this question. Using anonymized data from the German national transplantion registry, we extracted and evaluated information on the recipients and postmortem donors of kidneys that were allocated in Germany through Eurotransplant over the period 2006-2020. Data on 19 664 kidney transplantations in Germany from 2006 to 2020 were analyzed. The median waiting time for kidney transplantation was 5.8 years. Persons under age 18 waited a median of 1.7 years; persons aged 18 to 64, 7.0 years; and persons aged 65 and older, 3.8 years. Over the period of observation, postmortem kidneys were transplanted into 401 people of age 64 (2.0% of all organ recipients) and 1,393 people of age 65 (7.1% of all organ recipients). The difference in waiting times between allocation programs for persons under age 65 (ETKAS, "Eurotransplant Kidney Allocation System") and those aged 65 and older (ESP, "Eurotransplant Senior Program") increased over the period of observation, from 2.6 years in 2006-2010 to 4.1 years in 2017-2020. The rigid age limits in the current allocation rules for post-mortem kidney donations in Germany are prolonging the waiting times for transplants among patients aged 18 to 64. We think these rules need to be fundamentally reassessed.

Effects of the March 2021 Allocation Policy Change on Key Deceased-donor Kidney Transplant Metrics.

A major change to deceased-donor kidney allocation in the United States, Kidney Allocation System 250 (KAS250), was implemented on March 15, 2021. Evaluating the consequences of this policy on critical system performance metrics is critical to determining its success. We performed a retrospective analysis of critical performance measures of the kidney transplant system by reviewing all organs procured during a 4-y period in the United States. To mitigate against possible effects of the COVID-19 pandemic, Scientific Registry of Transplant Recipients records were stratified into 2 pre- and 2 post-KAS250 eras: (1) 2019; (2) January 1, 2020-March14, 2021; (3) March 15, 2021-December 31, 2021; and (4) 2022. Between-era differences in rates of key metrics were analyzed using chi-square tests with pairwise z-tests. Multivariable logistic regression and analysis of variations methods were used to evaluate the effects of the policy on rural and urban centers. Over the period examined, among kidneys recovered for transplant, nonuse increased from 19.7% to 26.4% (all between-era P < 0.05) and among all Kidney Donor Profile Index strata. Cold ischemia times increased (P < 0.001); however, the distance between donor and recipient hospitals decreased (P < 0.05). Kidneys from small-metropolitan or nonmetropolitan hospitals were more likely to not be used over all times (P < 0.05). Implementation of KAS250 was associated with increased nonuse rates across all Kidney Donor Profile Index strata, increased cold ischemic times, and shorter distance traveled.

Graft Survival of En Bloc Deceased Donor Kidneys Transplants Compared With Single Kidney Transplants.

The US Kidney Allocation System allocates en bloc deceased donor kidney grafts from donors <18 kg in sequence A along with single kidney transplants (SKTs) from kidney donor profile index (KDPI) top 20% donors. Although en bloc grafts outperform SKT grafts holding donor weight constant, it is unclear if en bloc grafts from the smallest pediatric donors perform the same as top 20% KDPI SKTs. Using the Scientific Registry of Transplant Recipients, we compared the donor characteristics and graft survival of en bloc grafts from the smallest donors (<8 kg) and from larger donors (≥8 kg) with SKTs by KDPI sequence for transplants performed in 2021. Larger donor en blocs had similar 1-y survival to sequence A SKTs estimated by the Kaplan-Meier method (96% versus 96%, P = 0.9), but the smallest donor en blocs had significantly shorter 1-y survival than those SKTs (80% versus 96%, P < 0.01). Using transplants from 2010 to 2012, the smallest donor en blocs had similar 10-y survival to sequence A SKTs (69% versus 64%, P = 0.3). These findings suggest that future updates of the Kidney Allocation System should include a score specific to pediatric donors to account for these differences in en bloc graft survival.

A2/A2B Deceased Donor Kidney Transplantation Using A2 Titers Improves Access to Kidney Transplantation: A Single-Center Study

Rationale and ObjectiveThe option for A2/A2B deceased donor kidney transplantation was integrated into the kidney allocation system in 2014 to improve access for B blood group waitlist candidates. Despite excellent reported outcomes, center uptake has remained low across the United States. Here we examined the effect of implementing an A2/A2B protocol using a cut off titer of ≤ 1:8 for IgG and 1:16 for IgM on blood group B kidney transplant recipients at a single center. Study DesignRetrospective observational study. Setting& Participants: Blood group B recipients of deceased donor kidney transplants at a single center from January 1, 2019 to December 2022. ExposureRecipients of deceased donor kidney transplants were analyzed based on donor blood type: A2/A2B vs. blood group compatible. Outcomes1 year patient survival, death censored allograft function, primary non-function, delayed graft function, allograft function as measured by serum creatinine and eGFR at 1 year, biopsy proven rejection, and need for plasmapheresis. Analytical ApproachComparison between the A2/A2B and compatible groups were performed using the Fisher test or the Chi-Square test for categorical variables and the nonparametric Wilcoxon Rank-Sum Test for continuous variables. ResultsA total of 104 blood type B patients received a deceased donor kidney transplant at our center during the study period, 49 (47.1%) of which received an A2/A2B transplant. Waiting time was lower in A2/A2B recipients compared to blood group compatible recipients (57.9 months vs. 74.7 months, p=0.01). A2/A2B recipients were more likely to receive a donor after cardiac death (24.5% vs 1.8%, p<0.05) and experience delayed graft function (65.3% vs. 41.8%). There were no observed differences in the average serum creatinine or eGFR at 1-month, 3-months, and 1-year post kidney transplantation, acute rejection, or primary non-function. LimitationsSingle center study. Small cohort size limiting outcome analysis. ConclusionsImplementation of an A2/A2B protocol increased transplant volumes of blood group B waitlisted patients by 83.6% while decreasing the waiting time for transplantation by 22.5% with similar transplant outcomes.

Differences in Racial and Ethnic Disparities Between First and Repeat Kidney Transplantation.

Recent data suggest patients with graft failure had better access to repeat kidney transplantation (re-KT) than transplant-naive dialysis accessing first KT. This was postulated to be because of better familiarity with the transplant process and healthcare system; whether this advantage is equitably distributed is not known. We compared the magnitude of racial/ethnic disparities in access to re-KT versus first KT. Using United States Renal Data System, we identified 104 454 White, Black, and Hispanic patients with a history of graft failure from 1995 to 2018, and 2 357 753 transplant-naive dialysis patients. We used adjusted Cox regression to estimate disparities in access to first and re-KT and whether the magnitude of these disparities differed between first and re-KT using a Wald test. Black patients had inferior access to both waitlisting and receiving first KT and re-KT. However, the racial/ethnic disparities in waitlisting for (adjusted hazard ratio [aHR] = 0.77; 95% confidence interval [CI], 0.74-0.80) and receiving re-KT (aHR = 0.61; 95% CI, 0.58-0.64) was greater than the racial/ethnic disparities in first KT (waitlisting: aHR = 0.91; 95% CI, 0.90-0.93; Pinteraction = 0.001; KT: aHR = 0.68; 95% CI, 0.64-0.72; Pinteraction < 0.001). For Hispanic patients, ethnic disparities in waitlisting for re-KT (aHR = 0.83; 95% CI, 0.79-0.88) were greater than for first KT (aHR = 1.14; 95% CI, 1.11-1.16; Pinteraction < 0.001). However, the disparity in receiving re-KT (aHR = 0.76; 95% CI, 0.72-0.80) was similar to that for first KT (aHR = 0.73; 95% CI, 0.68-0.79; Pinteraction = 0.55). Inferences were similar when restricting the cohorts to the Kidney Allocation System era. Unlike White patients, Black and Hispanic patients with graft failure do not experience improved access to re-KT. This suggests that structural and systemic barriers likely persist for racialized patients accessing re-KT, and systemic changes are needed to achieve transplant equity.

Cytomegalovirus Matching in Deceased Donor Kidney Allocation: Results From a U.S. National Simulation Model.

Cytomegalovirus (CMV) infects >60% of adults and can pose an independent risk factor for allograft loss and mortality in solid organ transplant recipients. The purpose of this study is to evaluate the impact of a nationwide implementation of CMV seromatching (donor/recipient: D-/R- and D+/R+) in the U.S. deceased donor kidney allocation system (KAS). Adult candidates on the U.S. kidney-only transplant waiting list and deceased donor kidneys offered to the U.S. transplant centers were considered. A discrete-event simulation model, simulating the pre-COVID-19 period from January 1, 2015, to January 1, 2018, was used to compare the performances of currently employed KAS-250 policy (without CMV matching) to various simulated CMV matching policies parameterized by calculated panel reactive antibody exception threshold. Outcomes included CMV serodistribution, waiting time, access to transplantation among various groups, transplant rate, graft survival, kidney discard rate, and antigen-mismatch distribution, stratified by CMV serostatus. CMV matching policy with a calculated panel reactive antibody exception threshold of 50% (namely, the CMV">50%" policy) strikes a better balance between benefits and drawbacks of CMV matching. Compared with KAS-250, CMV">50%" reduced CMV high-risk (D+/R-) transplants (6.1% versus 18.1%) and increased CMV low-risk (D-/R-) transplants (27.2% versus 13.1%); increased transplant rate for CMV R- patients (11.54 versus 12.57) but decreased for R+ patients (10.68 versus 10.48), yielding an increase in aggregate (11.09 versus 10.94); and reduced mean time to transplantation (by 6 wk); and reduced kidney discard rate (25.7% versus 26.2%). Our findings underscore the feasibility and potential advantages of a nationwide CMV seromatching policy in kidney transplantation.

A Quality Systems Perspective on Sensitization and Kidney Allocation System Changes.

A Quality Systems Perspective on Sensitization and Kidney Allocation System Changes.

Predictive value of donor kidney quality assessment and risk quantification scores on 5-year outcomes of deceased donor kidney transplantation.

Due to the excess demand for deceased donor kidneys, risk quantification scores were developed to help with kidney allocation. The kidney donor risk index (KDRI) is used in the US kidney allocation system. We currently use expanded criteria (UNOS) and Remuzzi scoring for allocation of deceased donor kidneys and the utility of KDRI in our cohort is unknown. We aim to evaluate the association of KDRI with relation to 5year graft and patient survival. Retrospective cohort study of 225 adults who received a deceased donor kidney transplant between 1 Nov 2005 and 30 June 2014. Patients were followed up for 5years or until graft-loss or death. Implant biopsies of donor kidneys were done and the Remuzzi score was calculated. The median age was 48 (IQR 42, 52.5) years and 50.7% were male. KDRI-USA, KDRI-THAI, and KDRI-AUST were found to have no correlation with 5year graft survival. Donor characteristics which define an expanded criteria donor kidney, not associated with 5year graft survival are age (p = 0.58), terminal creatinine (p = 0.71) and history of hypertension (p = 0.35). Donor cerebrovascular accident (CVA) as a cause of death (p = 0.02) and Remuzzi score were associated with graft survival at 5years, with 75.8% with Remuzzi score ≤ 3 vs 24.2% with Remuzzi score of > 3 achieving 5year graft survival (p = 0.001). The association of KDRI with graft and patient survival was not demonstrated in our cohort. Histological assessment of the transplant kidney remains the best method of predicting long-term survival during donor selection.

Association of Race and Ethnicity With High Longevity Deceased Donor Kidney Transplantation Under the US Kidney Allocation System

Rationale & ObjectiveThe US Kidney Allocation System (KAS) prioritizes candidates with ≤20% Estimated Post-Transplant Survival (EPTS) for high longevity kidneys defined by a ≤20% Kidney Donor Profile Index (KDPI). Use of EPTS in the KAS deprioritizes candidates with older age, diabetes, and longer dialysis durations. We assessed whether this use also disadvantages racial-ethnic minority candidates, who are younger but more likely to have diabetes and longer durations of kidney failure requiring dialysis. Study DesignObservational cohort study. Setting& Participants: Adult candidates for and recipients of kidney transplantation represented in the Scientific Registry of Transplant Recipients from January 2015 through December 2020. ExposureRace and ethnicity. OutcomesAge-adjusted assignment to ≤20% EPTS, transplantation of a ≤20% KDPI kidney, and post-transplant survival in longevity matched recipients by racial-ethnicity. Analytic ApproachMultivariable logistic regression, Fine-Gray competing risks survival analysis, and Kaplan-Meier and Cox Proportional Hazards methods. ResultsThe cohort included 199,444 candidates (7% Asian, 29% Black, 19% Hispanic/Latino, 43% White) listed for deceased donor kidney transplantation. Non-White candidates had significantly higher rates of diabetes, longer dialysis duration, and were younger than White candidates. Adjusted for age, Asian, Black, and Hispanic/Latino candidates had significantly lower odds of having a ETPS score ≤20% (OR 0.86, [0.81, 0.91], 0.52 [0.50, 0.54], and 0.49, [0.47, 0.51]), and were less likely to receive a ≤20% KDPI kidney (subHR 0.70 [0.66, 0.75], 0.89 [0.87, 0.92], and 0.73 [0.71, 0.76]), compared to White candidates. Among recipients with ≤20% EPTS scores transplanted with a ≤20% KDPI deceased donor kidney, Asian and Hispanic recipients had lower post-transplant mortality (HR 0.45 [0.27, 0.77], and 0.63 [0.47, 0.86]) and Black recipients had higher but not statistically significant post-transplant mortality (HR 1.22 [0.99, 1.52]) compared to White recipients. LimitationsProvider reported race-ethnicity data and 5-year post transplant follow-up period. ConclusionsThe US kidney allocation system is less likely to identify racial-ethnic minority candidates as having a ≤20% EPTS score which triggers allocation of high longevity deceased donor kidneys. These findings should inform the OPTN about how to remedy racial/ethnic disparities introduced through KAS’s current approach of allocating allografts with longer predicted longevity to recipients with longer estimated post-transplant survival.

A2/A2B to B kidney transplantation outcomes: A single center 7-year experience.

Data on long-term outcomes following A2/A2B to B kidney transplants since the 2014 kidney allocation system (KAS) changes are few. The primary aim of this study is to report our 7-year experience with A2/A2B to B kidney transplants and to compare post-transplant outcomes of A2/A2B to a concurrent group of B to B kidney transplants. Additionally, the study evaluates the impact of pre-transplant anti-A1 titers on survival outcomes in A2/A2B transplants. This retrospective, single-center analysis included all adults who received A2/A2B to B deceased donor kidney transplants from December 2014 to June 2021 compared to B to B recipients. The effects of pre-transplant IgM/IgG titers, stratified as ≤1:8 and ≥1:16, on death-censored, rejection-free, and overall graft survival were tested. Fifty-three A2/A2B and 114 B to B adults were included with a median follow-up time of 32 months. Overall graft survival, patient survival, and rejection-free graft survival did not differ between the two groups. There were no differences between the groups' overall kidney function values (p>.80) or their temporal trajectories (time by group interaction p>.11). Unadjusted death-censored graft survival was lower in A2/A2B to B compared to B recipients (p=.03), but the effect was not significant (p=.195) after adjusting for any readmissions (p=.96), rejection episodes (p<.001) or BK infection (p=.76). We did not detect an effect of pre-transplant titer group on death-censored (p=.59), rejection-free (p=.61), or overall graft survival (p=.26) CONCLUSIONS: A2/A2B to B kidney transplants have comparable overall patient and graft survival, rejection-free graft survival, and longitudinal renal function compared to B to B transplants at our center. Allograft survival outcomes were not significantly different between patients with low and high pre-transplant anti-A1 IgM/IgG titers.

Impact of the Kidney Allocation Revision on Access to Kidney Transplantation and Outcomes in the United States.

The 2014 Kidney Allocation System (KAS) revision aimed to enhance equity in organ allocation and improve patient outcomes. This study assesses the impacts of the KAS revision on renal transplantation demographics and outcomes in the United States. We conducted a retrospective study utilizing the Organ Procurement and Transplantation Network/Scientific Registry of Transplant Recipients (OPTN/SRTR) database from 1998 to 2022. We compared recipient and donor characteristics, and outcomes (graft failure and recipient survival) pre- and post-KAS revision. Post-KAS, recipients were significantly older (53 vs 48, P < .001) with an increase in Medicaid beneficiaries (7.3% vs 5.5%, P < .001). Despite increased graft survival, HR = .91 (95% CI 0.80-.92, P < .001), overall recipient survival decreased, HR = 1.06 (95% CI 1.04-1.09, P < .001). KAS revision led to greater racial diversity among recipients and donors, enhancing equity in organ allocation. However, disparities persist in graft failure rates and recipient survival across racial groups. The 2014 Kidney Allocation System revision has led to important changes in the renal transplantation landscape. While progress has been made towards increasing racial equity in organ allocation, further refinements are needed to address ongoing disparities. Recognizing the changing patient profiles and socio-economic factors will be crucial in shaping future policy modifications.

Progress made toward equitable transplantation in children and young adults with kidney disease.

Racial disparities in pediatric kidney transplantation have been well described over the last two decades and include disparities in preemptive transplantation, waitlisting, time from activation to transplantation, living donation, and graft outcomes. Changes to the organ allocation system including the institution of Share 35 in 2005 and the Kidney Allocation System (KAS) of 2014 have resulted in resolution of some, but not all racial-ethnic disparities. Despite overall improvements in time from waitlist activation to transplant, disparities remain in preemptive transplantation, time to waitlisting, and living donor transplantation. Although improving under the KAS, racial disparities remain in graft survival as well. Racial disparity in kidney transplant access and graft survival is an international problem within pediatric nephrology. Although the racial group affected may differ, various minoritized pediatric groups across the world are affected by transplant disparities. Social determinants of health including financial access, language barriers, and the presence of a healthy living donor play a role in mediating these disparities. Further investigation is needed to better understand and intervene upon modifiable social, biological, and cultural factors driving the remaining disparity in transplant outcomes.

Unrecognized opportunities: The landscape of pediatric kidney-paired donation in the United States.

Pediatric (age < 18 years) kidney transplant (KT) candidates face increasingly complex choices. The 2014 kidney allocation system nearly doubled wait times for pediatric recipients. Given longer wait times and new ways to optimize compatibility, more pediatric candidates may consider kidney-paired donation (KPD). Motivated by this shift and the potential impact of innovations in KPD practice, we studied pediatric KPD procedures in the US from 2008 to 2021. We describe the characteristics and outcomes of pediatric KPD recipients with comparison to pediatric non-KPD living donor kidney transplants (LDKT), pediatric LDKT recipients, and pediatric deceased donor (DDKT) recipients. Our study cohort includes 4987 pediatric DDKTs, 3447 pediatric non-KPD LDKTs, and 258 pediatric KPD transplants. Fewer centers conducted at least one pediatric KPD procedure compared to those that conducted at least one pediatric LDKT or DDKT procedure (67, 136, and 155 centers, respectively). Five centers performed 31% of the pediatric KPD transplants. After adjustment, there were no differences in graft failure or mortality comparing KPD recipients to non-KPD LDKT, LDKT, or DDKT recipients. We did not observe differences in transplant outcomes comparing pediatric KPD recipients to controls. Considering these results, KPD may be underutilized for pediatric recipients. Pediatric KT centers should consider including KPD in KT candidate education. Further research will be necessary to develop tools that could aid clinicians and families considering the time horizon for future KT procedures, candidate disease and histocompatibility characteristics, and other factors including logistics and donor protections.

Positive Long-Term Outcome of Kidney Allocation via Acceptable Mismatch Program in Highly Sensitized Patients

Introduction: Eurotransplant established the acceptable mismatch (AM) program to facilitate timely kidney transplantations of highly sensitized patients, but long-term granular clinical and immunological outcomes regarding overall graft survival and de novo DSA (dnDSA) formation are still intensively researched. The right choice of induction therapy in patients with differing immunological risk is not conclusively determined, as well as the impact of human leukocyte antigen (HLA) epitope matching on dnDSA formation. Methods: This monocentric, retrospective study analyzed 94 patients transplanted within the AM program between 2000 and 2019 compared to case-control matched cohorts of non- (PRA 0–5%; PRA-0) and intermediately sensitized (PRA 6–84%; PRA-6/84) patients transplanted through Eurotransplant Kidney Allocation System. Results: Estimated 10-year overall graft survival between the PRA-0 and AM cohorts was similar, whereas PRA-6/84 was significantly disadvantageous compared to PRA-0. Estimated 10-year incidence of antibody-mediated rejection rates was significantly lower in the PRA-0 group compared to AM and PRA-6/84 groups. Compared to the AM group, estimated incidence of de novo donor-specific antibody (dnDSA) was significantly lower in PRA-0 patients, with no differences between the AM and PRA-6/84 cohorts. The PRA-6/84 cohort was the only subgroup in which interleukin-2 receptor antagonist (IL2RA) induction was associated with longer overall graft survival, patient survival, and graft survival compared to depleting induction (ATG or OKT3). Broad HLA-A, -B, -DR mismatches (mmABDR) and HLA epitope mismatches determined by Eplets and PIRCHE-II were predictive for dnDSA formation in the total cohort, and the AM subgroup. Discussion: The high efforts expended on AM patients are justified to allow timely organ transplantation with acceptable risk profile and non-inferior outcomes. IL2RA induction in intermediately sensitized patients is associated with superior overall graft survival, patient survival, and graft survival compared to ATG/OKT3 induction, without negative effects on rejection episodes or dnDSA formation. In silico epitope matching might further help reduce dnDSA formation, particularly in high-risk AM patients.

A2/A2B to B deceased donor kidney transplantation in the Kidney Allocation System era

Kidney transplantation from blood type A2/A2B donors to type B recipients (A2→B) has increased dramatically under the current Kidney Allocation System (KAS). Among living donor transplant recipients, A2-incompatible transplants are associated with an increased risk of all-cause and death-censored graft failure. In light of this, we used data from the Scientific Registry of Transplant Recipients from December 2014 until June 2022 to evaluate the association between A2→B listing and time to deceased donor kidney transplantation (DDKT) and post-DDKT outcomes for A2→B recipients. Among 53 409 type B waitlist registrants, only 12.6% were listed as eligible to accept A2→B offers ("A2-eligible"). The rates of DDKT at 1-, 3-, and 5-years were 32.1%, 61.4%, and 72.1% among A2-eligible candidates and 14.1%, 29.9%, and 44.1% among A2-ineligible candidates, with the former experiencing a 133% higher rate of DDKT (Cox weighted hazard ratio (wHR) = 2.192.332.47; P < .001). The 7-year adjusted mortality was comparable between A2→B and B-ABOc (type B/O donors to B recipients) recipients (wHR 0.780.941.13, P = .5). Moreover, there was no difference between A2→B vs B-ABOc DDKT recipients with regards to death-censored graft failure (wHR 0.771.001.29, P > .9) or all-cause graft loss (wHR 0.820.961.12, P = .6). Following its broader adoption since the implementation of the kidney allocation system, A2→B DDKT appears to be a safe and effective transplant modality for eligible candidates. As such, A2→B listing for eligible type B candidates should be expanded.