OPTN/SRTR 2022 Annual Data Report: Pancreas.

The postpandemic recovery did not occur in pancreas transplantation as in other organs. The number of pancreas transplants in the United States decreased to 918 in 2022 from 963 in 2021. The number of simultaneous pancreas-kidney transplants decreased to 810 in 2022 from 820 in 2021, but the largest decrease was in pancreas transplant alone: 62 in 2022 compared with 92 in 2021. Pancreas-after-kidney transplants decreased to 46 in 2022 from 51 in 2021. The trend of increasing proportions of pancreas transplants in patients with type 2 diabetes seen over the past few years ended in 2022; there were 22.4% of such transplants in 2022 compared with 25.8% in 2021. The proportion of recipients older than 45 years decreased in 2022 as well. However, the proportions of candidates with type 2 diabetes and older candidates on the waiting list did not decrease. The number of pancreas donors decreased and the pancreas nonuse rate increased in 2022. Outcomes after pancreas transplant continued to improve, with an impressive 8.1% pancreas and 4.3% kidney graft failure rate for simultaneous pancreas-kidney transplant at 1 year in 2022. The proportion of pancreas transplants performed by medium-volume centers (11-24 transplants/year) returned to 37.2% in 2022 from a high of 48.3% in 2021, whereas the proportion of those done by large-volume centers (25 or more transplants/year) returned to 25.3% in 2022 from a low of 15.9% in 2021.

OPTN/SRTR 2022 Annual Data Report: Heart.

The number of heart transplants in the United States has continued to increase. Since 2011, pediatric heart transplants have increased 31.7% to 494 and adult heart transplants have increased 85.8% to 3,668 in 2022. The numbers of new candidates for pediatric and adult heart transplants have also increased, with 703 new pediatric candidates and 4,446 new adult candidates in 2022. Adult heart transplant rates continue to rise, peaking at 122.5 transplants per 100 patient-years in 2022; however, the pediatric heart transplant rate decreased to its lowest rate in the past decade, 104.2 transplants per 100 patient-years, a decrease of 13.9% from 121 transplants per 100 patient-years in 2011. Despite this, pretransplant mortality among pediatric candidates has decreased by 52.2%, from 20.8 deaths per 100 patient-years in 2011 to 10.0 deaths per 100 patient-years in 2022, but remains excessive for candidates younger than 1 year at 25.7 deaths per 100 patient-years. Among adult candidates, pretransplant mortality declined from 15 deaths per 100 patient-years in 2011 to 8.7 deaths per 100 patient-years in 2022. Since 2011, posttransplant mortality has been stable to slightly better; among recipients who underwent transplant in 2015-2017, the 1-, 3-, and 5-year pediatric survival rates were 93.7%, 89.2%, and 85.0%, respectively, and the adult survival rates were 91.3%, 85.7%, and 80.4%. Donor trends have been favorable, with an increase in the numbers of hearts recovered and growing numbers of hearts procured after circulatory death.

OPTN/SRTR 2022 Annual Data Report: Lung.

For the first time since the COVID-19 pandemic, the annual number of lung transplants performed in the United States increased. The year 2022, encompassed in this report, marks the last full calendar year where the Lung Allocation Score was used for ranking transplant candidates based on their estimated transplant benefit and donor lung allocation in the United States. In March 2023, a major change in transplant allocation policy occurred with the implementation of the Composite Allocation Score. Transplant rates have increased over the past decade, although there is variability among age, diagnosis, racial and ethnic, and blood groups. Over half of candidates received a lung transplant within 3 months of placement on the waiting list, with nearly 75% of candidates accessing transplant by 1 year. Pretransplant mortality rates remained stable, with approximately 13% of lung transplant candidates dying or being removed from the waiting list within a year of listing. Posttransplant survival remained stable; however, variability exists by age, diagnosis, and racial and ethnic groups.

OPTN/SRTR 2022 Annual Data Report: Deceased Organ Donation.

The Scientific Registry of Transplant Recipients uses data collected by the Organ Procurement and Transplantation Network to calculate metrics such as organs recovered per donor, organs transplanted per donor, and organs recovered for transplant but not transplanted (ie, nonuse). In 2022, there were 14,905 deceased donors, a 7.5% increase from 13,863 in 2021, and this number has been increasing since 2010. The number of deceased donor organs used for transplant increased to 37,334 in 2022, a 4.6% increase from 35,687 in 2021; this number has been increasing since 2012. The increase may be due in part to the rising number of deaths of young people amid the ongoing opioid epidemic. The number of organs transplanted included 10,130 left kidneys, 10,039 right kidneys, 298 en bloc kidneys, 922 pancreata, 8,847 livers, 83 intestines, 4,169 hearts, and 2,633 lungs. Compared with 2021, transplants of all organs except pancreata and intestines increased in 2022. In 2022, 3,563 left kidneys, 3,673 right kidneys, 156 en bloc kidneys, 366 pancreata, 965 livers, 4 intestines, 54 hearts, and 219 lungs were not used. These data suggest an opportunity to increase the number of transplants by reducing the number of unused organs. Despite the COVID-19 pandemic, there was no dramatic increase in the number of unused organs and there was an increase in the total numbers of donors and transplants.

OPTN/SRTR 2022 Annual Data Report: Vascularized Composite Allograft.

This year's chapter on vascularized composite allograft (VCA) encompasses reviews of data collected from 2014 (when VCA was included in the Final Rule) through 2022. The present Annual Data Report shows that the number of VCA recipients in the United States continues to be small and has remained consistent from the prior report. The data continue to be limited by sample size, with trends persistently demonstrating a predominance of White males in the young/middle-aged population as both donors and recipients for nonuterus VCA transplants, and White women younger than 35 years as the predominant recipients of uterus transplant. Similar to the 2021 report, there were only eight failed uterus grafts and one failed nonuterus VCA graft reported from 2014 through 2022. Standardization of definitions of success and failure as well as outcome measures for the different VCA types remain unmet needs in VCA transplantation.

Adjusting for race in metrics of organ procurement organization performance.

The Scientific Registry of Transplant Recipients has previously reported the effects of adjusting for demographic variables, including race, in the Centers for Medicare & Medicaid Services (CMS) organ procurement organization (OPO) performance metrics: donation rate and transplant rate. CMS chose not to adjust for most demographic variables other than age (for the transplant rate), arguing that there is no biological reason that these variables would affect the organ donation/utilization decision. However, organ donation is a process based on altruism and trust, not a simple biological phenomenon. Focusing only on biological impacts on health ignores other pathways through which demographic factors can influence OPO outcomes. In this study, we update analyses of demographic adjustment on the OPO metrics for 2020 with a specific focus on adjusting for race. We find that adjusting for race would lead to 8 OPOs changing their CMS tier rankings, including 2 OPOs that actually overperform the national rate among non-White donors improving from a tier 3 ranking (facing decertification without possibility of recompeting) to a tier 2 ranking (allowing the possibility of recompeting). Incorporation of stratified and risk-adjusted metrics in public reporting of OPO performance could help OPOs identify areas for improvement within specific demographic categories.

Augmenting the Unites States transplant registry with external mortality data: A moving target ripe for further improvement.

The Organ Procurement and Transplantation Network conducts a robust death verification process when augmenting the United States transplant registry with external sources of data. Process enhancements added over 35,000 externally verified deaths across waitlist candidates and transplant recipients for all organs beginning in April 2022. Ninety-four percent of added posttransplant deaths occurred beyond 5 years posttransplant, and over 74% occurred beyond 10 years. Deceased donor solid organ recipients transplanted from January 1, 2010, through October 31, 2020, were analyzed from January and July 2022 Organ Procurement and Transplantation Network Standard Transplant Analysis and Research and the Scientific Registry of Transplant Recipients Standard Analysis Files to quantify the impact of including vs excluding unverified deaths (not releasable to researchers) on posttransplant patient survival estimates. Across all organs, 1- and 5-year posttransplant survival rates were not substantially impacted; meaningful differences were observed in 10-year survival among kidney recipients. These findings bear important implications for anyone who utilized transplant registry data to examine long-term outcomes prior to the updated verification process. Users of transplant surveillance data should interpret results of long-term outcomes cautiously, particularly differences across subpopulations, and the transplant community should identify ways to improve data quality and minimize the reporting burden on transplant institutions.

OPTN/SRTR 2022 Annual Data Report: Kidney.

The year 2022 had continued successes and challenges for the field of kidney transplantation, as the community adapted to ongoing surges of the COVID-19 pandemic and broader geographic organ distribution. The total number of kidney transplants in the United States reached a record count of 26,309, driven by continued growth in deceased donor kidney transplants (DDKTs). The total number of candidates listed for DDKT rose slightly in 2022 but remained below 2019 listing levels, with 12.4% of candidates having been waiting 5 years or longer. Following the height of the COVID-19 pandemic, pretransplant mortality in 2022 declined across age, race and ethnicity, sex, and blood type groups. Pretransplant mortality continued to vary substantially by donation service area. The proportion of deceased donor kidneys recovered but not used for transplant (nonuse rate) rose to a high of 26.7% overall, with greater nonuse of biopsied kidneys (39.8%), kidneys from donors aged 55 years or older (54.7%), and kidneys with a kidney donor profile index (KDPI) of 85% or greater (71.3%). Nonuse of kidneys from donors who are hepatitis C virus (HCV) antibody positive rose to 30.2% but only slightly exceeded that of HCV antibody-negative donors. Disparities in access to living donor kidney transplant (LDKT) persist, especially for non-White and publicly insured patients. Delayed graft function continues an upward trend and occurred in 26.3% of adult kidney transplants in 2022. Five-year graft survival after LDKT compared with DDKT was 90.0% versus 81.4% for recipients aged 18-34 years and 80.8% versus 67.8% for recipients aged 65 years or older, respectively. The total number of pediatric kidney transplants performed in 2022 decreased to 705, its lowest point in the past decade; 502 (71.2%) were DDKTs and 203 (28.8%) were LDKTs. Among pediatric recipients, LDKT remains low, with continued racial disparities. The rate of DDKT among pediatric candidates has decreased by almost 25% since 2011. Congenital anomalies of the kidney and urinary tract remain the leading primary kidney disease diagnosis among pediatric candidates with a reported diagnosis. Most pediatric deceased donor recipients received a kidney from a donor with a KDPI of less than 35%. The rate of delayed graft function was 5.8% in 2022 and has been stable over the past decade. Long-term graft survival continues to improve, with superior outcomes for living donor transplant recipients.

OPTN/SRTR 2022 Annual Data Report: Liver.

In 2022, liver transplant activity continued to increase in the United States, with an all-time high of 9,527 transplants performed, representing a 52% increase over the past decade (2012-2022). Of these transplants, 8,924 (93.7%) were from deceased donors and 603 (6.3%) were from living donors. Liver transplant recipients were 94.5% adult and 5.5% pediatric. The overall size of the liver transplant waiting list contracted, with more patients being removed than added, although 10,548 adult patients still remained on the waiting list at the end of 2022. Alcohol-associated liver disease continued to be the leading diagnosis among both candidates and recipients, followed by metabolic dysfunction-associated steatohepatitis. Simultaneous liver-kidney transplant was the most common multiorgan combination, with 800 liver-kidney transplants performed in 2022; in addition, there were 303 new listings for kidney transplant via the safety net mechanism. Among adults added to the liver waiting list in 2021, 39.9% received a deceased donor liver transplant within 3 months; 45.7%, within 6 months; and 54.5%, within 1 year. Pretransplant mortality decreased to 12.3 deaths per 100 patient-years in 2022, although still 15.6% of removals from the waiting list were for death or being too sick for transplant. Graft and patient survival outcomes after deceased donor liver transplant improved, approximating pre-COVID-19 pandemic levels, with 5.1% mortality observed at 6 months; 6.8%, at 1 year; 12.7%, at 3 years; 19.8%, at 5 years; and 35.7%, at 10 years. Five-year graft and patient survival rates after living donor liver transplant exceeded those of deceased donor liver transplant. Candidates receiving model for end-stage liver disease exception points for hepatocellular carcinoma constituted 15.5% of transplants performed in 2022, with similar transplant rates and posttransplant outcomes compared to cases without hepatocellular carcinoma exception. In 2022, more pediatric liver transplant candidates were added to the waiting list and underwent transplant compared with either of the preceding 2 years, with an uptick in living donor liver transplant volume. Although pretransplant mortality has improved after the recent policy change prioritizing pediatric donors for pediatric recipients, still, in 2022, 50 children died or were removed from the waiting list for being too sick to undergo transplant. Posttransplant mortality among pediatric liver transplant recipients remained notable, with death occurring in 4.0% at 6 months, 6.0% at 1 year, 8.2% at 3 years, 9.8% at 5 years, and 13.9% at 10 years. Similar to adult living donor recipients, pediatric living donor recipients had better 5-year patient survival compared with deceased donor recipients.

OPTN/SRTR 2022 Annual Data Report: COVID-19.

This chapter updates the COVID-19 chapter from the 2021 Annual Data Report with trends through November 12, 2022, and introduces trends in recovery and use of organs from donors with a positive COVID-19 test. Posttransplant mortality and graft failure, which remained a concern in all organs at the last report due to the Omicron variant wave, have returned to lower levels in the most recent available data through November 2022. Use of organs from donors with a positive COVID-19 test has grown, particularly after the first year of the pandemic. Mortality due to COVID-19 should continue to be monitored, but most other measures have sustained their recovery and may now be responding more to changes in policy than to ongoing concerns with COVID-19.

The burden of COVID-19 mortality among solid organ transplant recipients in the United States.

Solid organ transplant recipients (SOTRs) have a heightened risk of adverse coronavirus disease 2019 (COVID-19) outcomes because of immunosuppression and medical comorbidity. We quantified the burden of COVID-19 mortality in United States (US) SOTRs. A sample of deaths documented in the US solid organ transplant registry from June 2020 through December 2022 was linked to the National Death Index to identify COVID-19 deaths and weighted to represent all SOTR deaths during the study period. Among 505 757 SOTRs, 57 575 deaths occurred, and based on the linkage, 12 396 (21.5%) were due to COVID-19. COVID-19 mortality was higher in males (mortality rate ratio [MRR]: 1.13), SOTRs aged 65 years and older (MRR: 1.50 in ages 65-74 vs ages 55-64 years), and non-Hispanic Black and Hispanic SOTRs (MRRs: 1.55 and 1.79 vs non-Hispanic White SOTRs). Kidney and lung recipients had the highest COVID-19 mortality, followed by heart, and then liver recipients. COVID-19 mortality also varied over time and across US states. Overall, SOTRs had a 7-fold increased risk of COVID-19 death compared to the US general population. SOTRs comprised 0.13% of the US population but accounted for 1.46% of all US COVID-19 deaths. SOTRs experience greatly elevated COVID-19 mortality. Clinicians should continue to prioritize COVID-19 prevention and treatment in this high-risk population.

"You don't know what you don't know": A qualitative study of informational needs of patients, family members, and living donors to inform transplant system metrics.

INTRODUCTION: Informational needs and potential use of transplant metrics, especially among patients, remain understudied and a critical component of the transplant community's commitment to patient-centered care. We sought to understand the perspectives and needs of patients, family members/caregivers, living donors, and deceased donor family members. METHODS: We examined decision-making experiences and perspectives on the needs of these stakeholder groups for data about the national transplant system among 58 participants of 14 focus groups and 6 interviews. RESULTS: Three major themes emerged: 1) informational priorities and unmet needs (transplantation system processes, long-term outcomes data, prelisting data, patient-centered outcomes, and ability to compare centers and regions); 2) challenges obtaining relevant and trustworthy information (patient burden and effort, challenges with medical jargon, and difficulty finding trustworthy information); and 3) burden of facing the unknown (stress and anxiety leading to difficulty processing information, challenges facing the transplant journey when you "don't know what you don't know"). CONCLUSION: Patient, family member, and living donor participation in shared decision-making has been limited by inadequate access to patient-centered information. New metrics and patient-facing data presentations should address these content gaps using best practices to improve understanding and support shared decision-making.

Seasonal Patterns of Living Kidney Donation in the United States From 1995 to 2019.

BACKGROUND: The number of living kidney donors in the United States has declined since 2005, with variations based on the donor-recipient relationship. The reasons for this decline are unclear, and strategies to mitigate declined donations remain elusive. We examined the change in donor number monthly (within-year) versus annually (between-years) to inform potentially modifiable factors for future interventions. METHODS: In this registry-based cohort analysis of 141 759 living kidney donors between 1995 and 2019, we used linear mixed-effects models for donor number per month and year to analyze between-year and within-year variation in donation. We used Poisson regression to quantify the change in the number of donors per season before and after 2005, stratified by donor-recipient relationship and zip-code household income tertile. RESULTS: We observed a consistent summer surge in donations during June, July, and August. This surge was statistically significant for related donors (incidence rate ratio [IRR] range: 1.12-1.33) and unrelated donors (IRR range: 1.06-1.16) across donor income tertiles. CONCLUSION: Our findings indicate lower rates of living kidney donation in non-summer months across income tertiles. Interventions are needed to address barriers to donation in non-summer seasons and facilitate donations throughout the year. Since the Organ Donor Leave Law provides a solid foundation for supporting year-round donation, extending the law's provisions beyond federal employees may mitigate identified seasonal barriers.

Impact of donor kidney biopsy on kidney yield and posttransplant outcomes.

Procurement biopsy is performed to determine kidney quality, but evidence supporting such association is poor. We investigated the impact of glomerulosclerosis percentage (GS%) on kidney yield and patient outcomes. Information on deceased kidney donors from July 1, 2017, to June 30, 2019, was collected. Association between GS% and kidney yield (number of kidneys procured per donor) and posttransplant graft and patient outcomes were studied. Maximal GS% and minimal GS% were calculated to determine the relationship between GS% and kidney yield; minimal GS% only for correlation with posttransplant outcomes. Multinomial logistic regression and Cox models with least absolute shrinkage and selection operator were used to analyze the association of GS% with kidney yield and posttransplant outcomes, respectively. The kidney yield was 1.63 when maximal GS% and minimal GS% were <5%, but was 0.88 when both GS% were >20%. The hazard ratio for graft failure 1 year after transplant was 1.05 when minimal GS% was 16% to 20%, but was 1.3 for GS% of >20%. The hazard ratio for mortality increased from 1 to 1.2 when minimal GS% reached >20%. In summary, higher GS% was associated with lower kidney yield and inferior posttransplant outcomes. Incorporation of GS% into Scientific Registry of Transplant Recipients models may reassure organ procurement organizations and transplant centers pursuing kidneys with relatively high GS% levels, thereby reducing kidney discard rates.

Impacts of removing race from the calculation of the kidney donor profile index.

The kidney donor risk index (KDRI), standardized as the kidney donor profile index (KDPI), estimates graft failure risk for organ allocation and includes a coefficient for the Black donor race that could create disparities. This study used the Scientific Registry of Transplant Recipients data to recalculate KDRI coefficients with and without the Black race variable for deceased donor kidney transplants from 1995 to 2005 (n = 69 244). The recalculated coefficients were applied to deceased kidney donors from 2015 to 2021 (n = 72 926) to calculate KDPI. Removing the Black race variable had a negligible impact on the model's predictive ability. When the Black race variable was removed, the proportion of Black donors above KDPI 85%, a category with a higher risk of organ nonuse, declined from 31.09% to 17.75%, closer to the 15.68% above KDPI 85% among non-Black donors. KDPI represents percentiles relative to all other donors, so the number of Black donors moving below KDPI 86% was roughly equal to the number of non-Black donors moving above KDPI 85%. Removing the Black donor indicator from KDRI/KDPI may improve equity without substantial overall impact on the transplantation system, though further improvement may require the use of absolute measures of donor risk KDRI rather than relative measures of risk KDPI.

OPTN/SRTR 2021 Annual Data Report: COVID-19.

This chapter updates the COVID-19 chapter from the 2020 Annual Data Report with trends through February 12, 2022, and introduces trends in COVID-19-specific cause of death on the waiting list and posttransplant. Transplant rates remain at or above prepandemic levels for all organs, indicating a sustained transplantation system recovery following the initial 3-month disruption due to the onset of the pandemic. Posttransplant mortality and graft failure remain a concern in all organs, with rates surging corresponding to waves of the pandemic. Waitlist mortality due to COVID-19 is also a concern, particularly among kidney candidates. While the recovery of the transplantation system has been sustained in the second year of the pandemic, ongoing efforts should focus on reducing posttransplant and waitlist mortality due to COVID-19, and graft failure.

OPTN/SRTR 2021 Annual Data Report: Deceased Organ Donation.

The Scientific Registry of Transplant Recipients uses data collected by the Organ Procurement and Transplantation Network to calculate metrics such as donation rate, organ yield, and rate of organs recovered for transplant but not transplanted (ie, nonuse). In 2021, there were 13,862 deceased donors, a 10.1% increase from 12,588 in 2020, and an increase from 11,870 in 2019; this number has been increasing since 2010. The number of deceased donor transplants increased to 41,346 transplants in 2021, a 5.9% increase from 39,028 in 2020; this number has been increasing since 2012. The increase may be due in part to the rising number of deaths of young people amid the ongoing opioid epidemic. The number of organs transplanted included 9,702 left kidneys, 9,509 right kidneys, 551 en bloc kidneys, 964 pancreata, 8,595 livers, 96 intestines, 3,861 hearts, and 2,443 lungs. Compared with 2019, transplants of all organs except lungs increased in 2021, which is remarkable as this occurred despite the COVID-19 pandemic. In 2021, 2,951 left kidneys, 3,149 right kidneys, 184 en bloc kidneys, 343 pancreata, 945 liver, 1 intestine, 39 hearts, and 188 lungs were not used. These numbers suggest an opportunity to increase numbers of transplants by reducing nonused organs. Despite the pandemic, there was no dramatic increase in number of nonused organs and there was an increase in total numbers of donors and transplants. The new Centers for Medicare & Medicaid Services metrics for donation rate and transplant rate have also been described and vary across organ procurement organizations; the donation rate metric varied from 5.82 to 19.14 and the transplant rate metric varied from 18.7 to 60.0.

OPTN/SRTR 2021 Annual Data Report: Lung.

The number of lung transplants has continued to decline since 2020, a period that coincides with the onset of the COVID-19 pandemic. Lung allocation policy continues to undergo considerable change in preparation for adoption of the Composite Allocation Score system in 2023, beginning with multiple adaptations to the calculation of the Lung Allocation Score that occurred in 2021. The number of candidates added to the waiting list increased after a decline in 2020, while waitlist mortality has increased slightly with a decreased number of transplants. Time to transplant continues to improve, with 38.0% of candidates waiting fewer than 90 days for a transplant. Posttransplant survival remains stable, with 85.3% of transplant recipients surviving to 1 year; 67%, to 3 years; and 54.3%, to 5 years.

OPTN/SRTR 2021 Annual Data Report: Heart.

The past 5 years have posed challenges to the field of heart transplantation. The 2018 heart allocation policy revision was accompanied by anticipated practice adjustments and increased use of short-term circulatory support, changes that may ultimately serve to advance the field. The COVID-19 pandemic also had an impact on heart transplantation. While the number of heart transplants in the United States continued to increase, the number of new candidates decreased slightly during the pandemic. There were slightly more deaths following removal from the waiting list for reasons other than transplant during 2020, and a decline in transplants among candidates listed as status 1, 2, or 3 compared with the other statuses. Heart transplant rates decreased among pediatric candidates, most notably among those younger than 1 year. Despite this, pretransplant mortality has declined for both pediatric and adult candidates, particularly candidates younger than 1 year. Transplant rates have increased in adults. The prevalence of ventricular assist device use has increased among pediatric heart transplant recipients, while the prevalence of short-term mechanical circulatory support, particularly intra-aortic balloon pump and extracorporeal membrane oxygenation, has increased among adult recipients.

OPTN/SRTR 2021 Annual Data Report: Pancreas.

The number of pancreas transplants in the United States was largely unchanged in 2021 at 963 transplants compared with 962 in 2020, showing that recovery from the COVID-19 pandemic was not as pronounced in pancreas transplantation as in other organs. The number of simultaneous pancreas-kidney transplants (SPKs) decreased from 827 to 820, whereas the number of pancreas-after-kidney transplants and pancreas transplants alone increased marginally to compensate. The proportion of patients with type 2 diabetes on the waiting list increased to 22.9% in 2021, compared with 20.1% in 2020. Consequently, the proportion of transplants in patients with type 2 diabetes increased from 21.3% in 2020 to 25.9% in 2021. The proportion of transplants in older recipients (aged 55 years or older) also increased to 13.5% in 2021 from 11.7% in 2020. Outcomes after SPK continue to be the best of the three categories of pancreas transplants: 1-year graft failure for kidney at 5.7% and pancreas at 10.5% for transplants performed in 2020. The proportion of pancreas transplants performed by medium-volume centers (11-24 transplants per year) increased sharply to 48.3% in 2021 from 35.1% in 2020, with a corresponding decrease in transplants in large-volume centers (25 or more transplants per year) to 15.9% in 2021 from 25.7% in 2020.