Effects of Donor-Recipient Race Matching on Kidney Transplant Survival

Abstract

Background

Given the scarcity of donor organs in the United States, the ability to prolong kidney transplant graft survival is a significant public health concern. Although it has been suggested that donor-recipient race-matching could improve kidney transplant outcomes, findings of previous studies are inconsistent. Therefore, the objective of this study was to conduct a systematic review examining the relationship between Black and White donor-recipient race-matching and graft and patient survival in adult primary kidney transplant recipients.

Material/Methods

Ovid Medline and Embase literature searches were conducted from earliest index date through October 2024. The following data were extracted and summarized: study characteristics, patient population characteristics, and findings associated with graft and patient survival. Quality assessment and magnitude of effects were evaluated, and Grading of Recommendations Assessment, Development and Evaluation (GRADE) was used to determine evidence certainty.

Results

Of 4676 citations, 7 studies met inclusion criteria. Two studies reported Black-Black donor-recipient pairings, 2 studies reported Black-White donor-recipient pairings, and 3 studies reported White-Black donor-recipient pairings were at significantly higher risk for graft failure than the reference group; however, effect magnitude was small. Studies found the relationship between race-matching and patient survival was not statistically significant. Per GRADE, evidence concerning graft and patient survival is of low certainty or quality.

Conclusions

Studies generally found no differences in patient survival, and although Black-Black, Black-White, and White-Black donor-recipient pairings were associated with decreased graft survival in some studies, effects were small and likely clinically irrelevant. Further investigation of modifiable factors influencing graft survival is needed.

Introduction

Given the scarcity of donor organs in the United States, the ability to prolong kidney transplant graft survival is a significant public health concern, particularly among Black transplant recipients whose survival rates continue to lag behind those of White recipients [1]. Investigators have suggested race-matching could be predictive of solid-organ transplant outcomes because donors “of similar ethnographic origin could provide greater physiologic and genetic similarities between the organ donor and recipient” [2,3]. However, findings of prior studies of race-matching in kidney transplant populations are not consistent.

More specifically, some prior studies found positive associations between race-matching and kidney transplant outcomes, while other studies did not [2–10]. For example, Locke et al [4] found that race-matched adult Black kidney transplant recipients experienced greater graft and patient survival than did Black recipients who received White donor kidneys. In contrast, LeClaire et al [2] found that compared with race-mismatched recipients, race-matched adult Black kidney transplant recipients had worse graft survival but no significant differences in patient survival [2]. Callender et al [6,7] found that race-matched and mismatched Black kidney transplant recipients and race-mismatched White recipients had worse graft survival than did race-matched White recipients. Patient survival outcomes were mixed, with White recipients who received Black donor kidneys at increased risk of mortality and Black recipients who received White donor kidneys at decreased risk of mortality than race-matched White recipients, while there was no significant difference versus race-matched Black recipients [7]. Yet another study found no significant differences in 1-year graft survival in race-matched Black kidney transplant recipients, compared with Black recipients who received White donor kidneys [5].

Due to conflicting evidence and to better understand the effects of race-matching on kidney transplant outcomes, a systematic review that evaluates and synthesizes the existing evidence would be valuable; however, such a synthesis has not yet been published, representing a gap in the literature. Thus, the objective of this study was to address this gap and conduct a systematic review examining the relationship between Black and White donor-recipient race-matching (compared with mismatching, defined as donor and recipient being of different races) and the outcomes of graft and patient survival in adult primary kidney transplant recipients. We hypothesized that the preponderance of evidence would support race-matching is not significantly associated with graft or patient survival among adult kidney transplant recipients. If the hypothesis is substantiated, this would lend further support to the 2024 decision to remove the Black race coefficient from the Kidney Donor Profile Index (KDPI), an algorithm intended to predict quality of a donor organ and assist in determining suitability of an organ match [11,12].

Material and Methods

The methodology of this systematic review was based on PRISMA 2020 and the Cochrane Handbook for Systematic Reviews of Interventions [13,14]. Literature search strategies were developed in consultation with an academic health center librarian. Searches were conducted of Ovid Medline and Embase (accessed through institutional subscription) from earliest index date (1946 and 1974, respectively) through October 31, 2024, to allow for the most complete search possible. Ovid Medline (2025) and Embase (2025 Elsevior Limited) were selected as search databases because both are comprehensive biomedical literature databases of journals in which studies pertaining to kidney transplant are most likely to be published. While there is some degree of overlap between the databases, both were included in the systematic review to capture content that may have only been located in one or the other database. Specifically, OVID Medline indexes approximately 5600 journals and Embase indexes more than 8400 journals (of which, nearly 3400 are unique to Embase) [15,16]. Although comprehensive, an acknowledged limitation of the search databases is that they may not include all literature relevant to this systematic review.

Broad search strategies were used, as donor-recipient race-matching may have been included in studies but not as the primary focus. Combinations of search terms (keywords) and Medical Subject Headings (MeSH) terms included (but were not limited to) organ transplant, racial/ethnic groups, outcomes, survival, mortality, match, mismatch, concordant, and discordant. Multi-step search strategies or queries were adapted for each database. For example, one step in the Embase search query was denoted as: ((cross* OR across OR between*) NEAR/3 (race OR races OR racial* OR ethni* OR ethno*)) OR ((match* OR mismatch* OR concordan* OR nonconcordan* OR discordan* OR compatib* OR noncompatib* OR incompatib* OR congruen* OR incongruen* OR discongruen* OR conflict* OR nonconflict* OR harmon* OR consisten* OR inconsisten* OR disparat* OR similar* OR dissimilar* OR converg* OR diverg* OR variab* OR variat*) NEAR/10 (race OR races OR racial* OR ethni* OR ethno*)). Comprehensive search strategies are available upon request to the corresponding author. One reviewer (CS) assessed the search results provided by the academic health center librarian to remove duplications (Figure 1).

Figure 1.

Flowchart of study inclusion and exclusion. ^a Non-quantitative studies/articles were defined as qualitative studies, review articles, systematic reviews, commentaries, perspectives, editorials, letters to the editor, conference abstracts, etc. ^b Study population did not include adult primary kidney transplant recipients or included patients who received multiple organ transplants or included patients who were retransplanted. ^c Study did not examine donor-recipient race matching/mismatching, and/or did not examine outcomes of interest, and/or did not analyze independent relationship between donor-recipient race matching/mismatching and outcomes of interest (this includes situations in which donor-recipient race matching/mismatching was controlled for in analysis and there was insufficient detail to interpret independent association; also includes situations in which statistical significance testing was not conducted). ^d Study initially met inclusion criteria, but the database (study population) and study time period overlapped with 1 or more other studies that met inclusion criteria. In this instance, studies were ultimately selected for inclusion based on not have overlapping populations and time periods and a combination of considerations including longer study time period, larger study population, and/or examining both outcomes of interest (graft and patient survival). Eight overlapping studies meeting inclusion criteria utilized the United Network for Organ Sharing/Organ Procurement & Transplantation database or Scientific Registry of Transplant Recipients, with 2 studies ultimately included; 2 overlapping studies utilized the University of California Los Angeles Transplant Registry, with 1 study ultimately included. (Microsoft 365 Word and PowerPoint.) Flowchart template from: Page MJ, McKenzie JE, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, et al. The PRISMA 2020 statement: An updated guideline for reporting systematic reviews. BMJ 2021;372:n71. doi: 10.1136/bmj.n71.

Study Selection

One reviewer (CS) conducted an initial screening of literature search results to exclude non-quantitative studies, such as qualitative studies, commentaries, and editorials (Figure 1). Two reviewers (MCB and CS) then independently conducted the study inclusion process, described in Figure 1. Peer-reviewed studies were included if they met all of the following criteria: (1) U.S. study (patient) population; (2) study population composed of adults (18 years or older) who had undergone primary kidney transplant; (3) quantitative in nature with statistical significance testing; (4) study included at least one Black and/or White race-matched donor-recipient pairing; and (5) analyzed the independent relationship between donor-recipient race-matching and mismatching and outcomes of interest (graft survival/failure and/or patient survival/mortality). In the assessment of eligibility, studies were excluded if they included a non-U.S. patient population, did not focus on adult primary kidney transplant patients, and did not assess the independent relationship between Black and/or White donor-recipient race-matching and graft and/or patient survival. Additionally, and as described in Figure 1, to eliminate redundant populations, studies that otherwise met inclusion criteria were excluded due to overlapping study databases (populations) and/or time periods. Inclusion among studies using the same database was based on not having overlapping populations and time periods, and a combination of considerations, including having a longer study time period, larger study population, and/or examining both outcomes of interest (graft and patient survival). There was no disagreement on included studies between the 2 reviewers.

Data Extraction

Two reviewers (MCB and CS) independently used a standardized data extraction tool. Data were collected concerning study characteristics (eg, study design, sample size), patient population characteristics (eg, age, sex, race/ethnicity, donor-recipient pairings, donor type), type of analysis (bivariate, multivariate), and study findings. We primarily focused on Black and White donor-recipient race-matched pairings (eg, Black-Black, White-White) and race-mismatched pairings (eg, Black-White, White-Black), as they represent the largest adult kidney transplant populations (approximately 80% of adult kidney transplant recipients in the U.S. are Black or White) [17]. Other racial and ethnic populations were not consistently represented in studies. When necessary to resolve disagreement, as occurred with 3 studies, reviewers met and reconciled extracted data [14]. A cross-check of extracted data was performed on all included studies as a quality control measure.

When extracting data concerning study findings, the following transplant outcomes in association with donor-recipient race-matching/mismatching were recorded: graft survival (or graft failure/loss) and patient survival (or patient mortality). Additionally, data were collected concerning length of the follow-up period, reference or comparator group (eg, White-White donor-recipient pairing was commonly used as the reference group across studies), and statistical significance of the association between transplant outcome and donor-recipient race-matching. For statistically significant associations between donor-recipient race-matching and transplant outcomes (ie, graft survival/failure, patient survival/mortality), effect measures (eg, hazard, odds, risk ratios) and direction of the association were described (for example, graft or patient survival was better or worse among race-matched vs mismatched recipients). Study data are available upon request to the corresponding author.

Quality Appraisal

Two reviewers (MCB and CS) independently conducted a quality assessment of included studies using the Quality Assessment of Observational Cohort and Cross-Sectional Studies tool published by the National Institutes of Health [18]. The tool includes a series of questions concerning whether a given study was designed to address risks of bias and internal validity threats. A study was rated as “good quality” if it addressed at least 70% of risks, “fair quality” if it addressed at least 50% of risks, and “poor quality” if it addressed less than 50% of risks [19,20]. To resolve disagreements, as occurred with 5 studies, reviewers met and reconciled the quality assessment [14].

Certainty of Evidence Assessment

Certainty of evidence for each outcome of interest (graft survival/loss and patient survival/mortality) was assessed using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) guideline [21]. According to Guyatt et al, “quality of evidence” for systematic reviews “reflects the extent of confidence that an estimate of effect is correct” [21]. Per GRADE, there are 4 levels of certainty evidence (high, moderate, low, very low), with starting values based on study design. Specifically, randomized trials begin as high-certainty (high-quality) evidence, while observational studies begin as low-certainty (low-quality) evidence [21]. There are 5 factors that can decrease certainty of evidence: study limitations, inconsistency of results, indirectness of evidence, imprecision, and publication bias [21]. Likewise, there are 3 factors that can increase certainty of evidence: large magnitude of effect, plausible confounding, and dose-response gradient [21]. Each included study was assessed by 2 reviewers (MCB and CS) using GRADE by first determining study design and then considering the factors that can decrease or increase certainty of evidence.

Data Synthesis

Data were synthesized using Microsoft Excel (Microsoft Corporation, Redmond, WA). Study characteristics and outcomes were summarized using frequency counts. Of note, multiple studies examined the association between donor-recipient race-matching and outcomes of interest at different time points after transplantation. Frequency counts summarized results of multivariate analysis (or bivariate analysis, when multivariate was not conducted) and overall finding (if available, rather than multiple time periods in the same study). Interpretation of magnitude of effects, which were primarily hazard ratios or risk ratios, was based on Lu et al [22] and Chen et al [23]. For example, Lu et al [22] suggested hazard ratios of 1.16–1.68 indicate small effects, and Chen et al [23] suggested odds ratios of 1.46–1.68 indicate small effects.

Results

Of 4676 citations identified in the literature search, 7 studies were included in the systematic review (Figure 1). The design of all 7 studies was classified as observational or case-control, with 4 using large registry or database data (Table 1). No randomized controlled trials met inclusion criteria. All 7 studies reported graft survival or loss outcomes. Three studies reported patient survival or mortality outcomes. In the quality assessment (Table 2), all 7 studies were rated as good or fair.

Table 1.

Description of graft and patient survival outcomes of included studies (n=7) [2,5,24–28].

Study	Database/ transplant center	Study dates	Total study (kidney transplant recipient) population	Recipient characteristics	Donor type	Graft survival or loss outcomes as specified in study	Patient survival or mortality outcomes as specified in study
Gaston et al 1992 [5a]	University of Alabama at Birmingham	February 1985 to July 1990	642 (Group 1 [triple IST, transplanted 1985–1987]: n=276; Group 2 [quadruple IST, transplanted 1987–1990]: n=366)	Male: 402 (Group n=1, 176; Group 2, n=226) Female: 240 (Group 1, n=100; Group 2, n=140) Age: Group 1 mean 39.8 years, SD 0.6; Group 2 mean 40.1 years, SD 0.6 Race: White (n=343 [Group 1, n=163; Group 2, n=180]); Black (n=299 [Group 1, n=113; Group 2, n=186)	Deceased	Bivariate analysis: Graft survival: 1-year survival rates in Group 2: Black-Black (n=25) vs White-Black D/R pairing (n=159): NS Survival from at least 3 months to 36 months post-transplant: Group 1, Black recipients “fared worse” than White recipients, regardless of donor race (p values not provided); Group 2, D/R pairings were NS	Not applicable
LeClaire et al 2021 [2a]	OPTN/UNOS	1999–2018	265,177	Gender and age data not provided Race: White (n=134,972); Black (n=69,470)	Deceased, living related, living unrelated	Multivariate analysis: Graft survival (1-year post-transplant): Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: NS Graft survival (3-years post-transplant): Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: decreased survival Graft survival (5-years post-transplant): Race-matched vs Mismatched-White: increased survival Race-matched vs Mismatched-Black: decreased survival Graft survival (10-years post-transplant): Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: decreased survival Overall graft survival (time post-transplant not specified): Race-matched vs Mismatched-White: NS [HR: 0.958 (95% CI 0.913–1.006), p=.084] Race-matched vs Mismatched-Black: decreased survival [HR: 1.118 (95% CI 1.066–1.172), p<.001]	Multivariate analysis: Patient survival (1-year post-transplant): Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: NS Patient survival (3-year post-transplant) Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: decreased survival Patient survival (5-year post-transplant): Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: NS Patient survival (10-year post-transplant): Race-matched vs Mismatched-White: NS Race-matched vs Mismatched-Black: NS Overall patient survival (time post-transplant not specified): Race-matched vs Mismatched-White: NS [HR: 1.024 (95% CI 0.973–1.078), p=.368] Race-matched vs Mismatched-Black: NS [HR: 1.056 (95% CI 0.999–1.116), p=.056]
Meier-Kriesche et al 2000 [24]	USRDS	October 1, 1988 to June 30, 1997	59,509	Male: 25,675 Female: 16,518 Age: 18–49 years, n=28,188 (mean 36.3, SD 8.1); 50–64 years, n=11,669 (mean 56.3, SD 4.2); 65 years and older, n=2336 (mean 68.1, SD 2.9) Race/ethnicity: White (n=42,193); Black (n not provided) (Note: gender and age data provided for White recipients only)	Deceased (n=31,213) Living (n=10,980) (Note: data provided for White recipients only)	Multivariate analysis: Chronic allograft failure (at least 6 months post-transplant to date of graft loss or death or study end date): Black-White D/R pairing vs White-White D/R pairing: increased risk [RR: 1.26, 95% CI 1.12–1.421; p=.0001]	Not applicable
Opelz et al 1977 [25a]	Over 100 North American transplant centers	January 1970 to December 1975	5969	Gender and age data not provided Race: White (n=5251); Black (n=1134)	Deceased: White, n=3581; Black, n=978 Living related: 1826 (White, n=1670; Black, n=156)	Bivariate analysis: Graft survival (deceased donor pairings only): White-Black D/R pairing: 1-year and 3-year post-transplant, decreased survival Black-White D/R pairing: 1-year and 3-year post-transplant, decreased survival Black-Black D/R pairing: 1-year and 2-year post-transplant, decreased survival (vs White-White D/R reference group)	Bivariate analysis: Patient survival (deceased donor pairings only): Statistical association described as being independent of recipient’s race. Recipients (regardless of race) of White donor organs had significantly better patient survival than recipients (regardless of race) of Black donor organs at 1 year, 2 years, and 3 years post-transplant
Perdue & Terasaki 1982 [26a]	UCLA International Transplant Registry	1968–1981	14,211	Gender and age data not provided Race: White (n=11,582); Black (n=2335)	Deceased (n=10,928); Living Related (n=3283)	Bivariate analysis: Graft survival (deceased donor pairings only): Black recipients “tend to have lower graft survival rates in all classes of transplants” compared to White recipients, except for grafts from Black donors (no p values reported). “The most highly significant differences in survival … are between” White donor groups. White recipients (White-White D/R pairings) have significantly higher graft survival rates than Black recipients (White-Black D/R pairings) at 3 months, 1 year, and 5 years post-transplant. Black deceased donor kidneys had lower graft survival rates than White deceased donor kidneys in all recipient races (no p values reported)	Bivariate analysis: Patient survival (deceased donor pairings only): Patient survival rates (3 months, 1 year, and 5 years post-transplant) “were essentially the same” but rates for the White-Black D/R pairing were “somewhat lower” than rates for White recipients. No p values reported
Tiwari et al 1987 [27a]	UCLA International Transplant Registry	January 1983 (end date not provided in study)	5234 (however, 6396 “cases” are reported in Table 1 of article [3904 CsA group, 2492 no CsA group])	Gender and age data not provided Race: White (n=4471); Black (n=821)	Deceased	Bivariate analysis: Grant survival (1-year post-transplant): White-Black vs White-White D/R pairing: decreased survival	Not applicable
Vincenti et al 1978 [28a]	University of California, San Francisco	January 1970 to March 1977	510	Male=285 Female=225 Age: mean 34 years, SD 6 Race/ethnicity: White (n=386); Black (n=97)	Deceased	Bivariate analysis: Graft survival (2 years post-transplant): White-White vs Mismatched-White D/R pairing: NS Black-Black vs Mismatched-Black D/R pairing: NS	Not applicable

CI – confidence interval; CsA – cyclosporine; D/R – donor-recipient; HR – hazard ratio; IST – immunosuppressant therapy; NS – not significant; OPTN – Organ Procurement and Transplantation Network; RR – risk ratio; SRTR – Scientific Registry of Transplant Recipients; UCLA – University of California, Los Angeles; UNOS – United Network for Organ Sharing; USRDS – United States Renal Data System.

^aCaveat: Study did not specify if patient population included pediatrics.

Table 2.

Quality assessment of included observational and case-control studies (n=7) [2,5,24–28^{a b}].

Studies	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Q8	Q9	Q10	Q11	Q12	Q13	Q14c	Rating
Gaston et al 1992 [5]	0	1	NA	1	0	1	1	NA	1	NA	1	NA	NA	1	G
LeClaire et al 2021 [2]	1	0	NA	1	0	1	1	NA	1	NA	1	NA	NA	1	G
Meier-Kriesche et al 2000 [24]	1	1	NA	1	0	1	1	NA	1	NA	1	NA	NA	1	G
Opelz et al 1977 [25]	1	0	NA	1	0	1	1	NA	1	NA	1	NA	NA	0	F
Perdue & Terasaki 1982 [26]	1	0	NA	1	0	1	1	NA	1	NA	1	NA	NA	0	F
Tiwari et al 1987 [27]	1	0	NA	CD	0	1	1	NA	1	NA	1	NA	NA	1	F
Vincenti et al 1978 [28]	1	1	NA	1	0	1	1	NA	1	NA	1	NA	NA	0	G

^aResponse categories: 1 – Yes; 0 – No; CD – cannot determine; F – fair quality; G – good quality; NA – not applicable; NR – not reported; P – poor quality.

^bStudies addressing greater than 70% of risks of bias and threats to internal were considered as good quality, studies addressing 50–70% of items were considered as fair quality, and studies addressing less than less than 50% of items were considered poor quality.

Questions:

Q1: Was the research question or objective in this paper clearly stated?

Q2: Was the study population clearly specified and defined?

Q3: Was the participation rate of eligible persons at least 50%?

Q4: Were all the subjects selected or recruited from the same or similar populations (including the same time period)? Were inclusion and exclusion criteria for being in the study prespecified and applied uniformly to all participants?

Q5: Was a sample size justification, power description, or variance and effect estimates provided?

Q6: For the analyses in this paper, were the exposure(s) of interest measured prior to the outcome(s) being measured?

Q7: Was the timeframe sufficient so that one could reasonably expect to see an association between exposure and outcome if it existed?

Q8: For exposures that can vary in amount or level, did the study examine different levels of the exposure as related to the outcome (e.g., categories of exposure, or exposure measured as continuous variable)?

Q9: Were the exposure measures (independent variables) clearly defined, valid, reliable, and implemented consistently across all study participants?

Q10: Was the exposure(s) assessed more than once over time?

Q11: Were the outcome measures (dependent variables) clearly defined, valid, reliable, and implemented consistently across all study participants?

Q12: Were the outcome assessors blinded to the exposure status of participants?

Q13: Was loss to follow-up after baseline 20% or less?

Q14: Were key potential confounding variables measured and adjusted statistically for their impact on the relationship between exposure(s) and outcome(s)? (^c Of note, adjustment for confounding variables may not have occurred in analysis of race-matching or mismatching.)

Included study sample sizes ranged from 510 to 265 177, with 5 studies having samples greater than 5000 (Table 1). Three of 7 studies provided data on patient sex. Three studies included only deceased donor transplants, and the remaining 4 included deceased and living donor transplants. Among donor-recipient racial pairings, Black-Black pairings were included in 6 of 7 studies, White-White pairings in all 7 studies, Black-White pairings in 5 studies, and White-Black pairings in 5 studies. Mismatched-White and mismatched-Black donor-recipient pairings were included in 2 studies.

Table 1 summarizes the outcomes of each of the 7 included studies [2,5,24–28]. Five of 7 studies reported statistically significant associations between race-matching or mismatching and the graft survival/failure outcome (Tables 1, 3). Two studies conducted multivariate analysis to control for confounding variables, with small magnitude of effects (hazard/risk ratios of 1.118 and 1.26). GRADE indicates the evidence is low-certainty (low-quality), as the studies are observational. Two of 6 studies reported Black-Black donor-recipient pairings were at significantly higher risk for graft failure, or decreased graft survival, compared with the reference group (White-White or race-mismatched pairing). Three of 5 studies reported White-Black donor-recipient pairings were at significantly higher risk for graft failure versus White-White pairing, while 1 study did not find a statistically significant relationship versus Black-Black pairing. Two of 5 studies reported Black-White donor-recipient pairings were at significantly higher risk for graft failure, or decreased graft survival, compared with the White-White reference group. Two of 3 studies found the relationship between race-matching and patient survival was not significant, while the third found patient survival was independent of recipient race, with White donor organs associated with increased patient survival, compared with Black donor organs, regardless of recipient race (Tables 1, 4).

Table 3.

Graft survival outcomes (n=7) [2,5,24–28].

Study	Reference group (D/R pairing)	D/R pairing	Graft survival or loss outcome, D/R pairing vs reference group
Gaston et al 1992 [5a]	White-Black	Black-Black	p=.07 (NS)
LeClaire et al 2021 [2a]	White-White	Mismatched-White	NS [HR: 0.958 (95% CI 0.913–1.006), p=.084]
	Black-Black	Mismatched-Black	Black-Black pairing had decreased graft survival [HR: 1.118 (95% CI 1.066–1.172), p<.001]
Meier-Kriesche et al 2000 [24]	White-White	Black-White	Black-White pairing had increased risk of graft loss [RR: 1.26, 95% CI 1.12–1.421; p=.0001]
Opelz et al 1977 [25a]	White-White	Black-Black	Black-Black pairing had decreased graft survival (p<.001)
	White-White	Black-White	Black-White pairing had decreased graft survival (p<.005)
	White-White	White-Black	White-Black pairing had decreased graft survival (p<.001)
Perdue & Terasaki 1982 [26a]	White-White	White-Black	White-Black pairing had decreased graft survivalb
Tiwari et al 1987 [27a]	White-White	White-Black	White-Black pairing had decreased graft survivalb
Vincenti et al 1978 [28a]	White-White	Mismatched-White	NS (p value not reported)
	Black-Black	Mismatched-Black	NS (p value not reported)

CI – confidence interval; D/R – donor-recipient; HR – hazard ratio; NS – not significant; RR – risk ratio.

^aCaveat: Study did not specify if patient population included pediatrics;

^bArticle indicates statistical significance but does not report P values.

Table 4.

Patient survival outcomes (n=3) [2,25,26].

Study	Reference group (D/R pairing)	D/R pairing	Patient survival or mortality outcome, D/R pairing vs reference group
LeClaire et al 2021 [2a]	White-White	Mismatched-White	NS [HR: 1.024 (95% CI 0.973–1.078), p=.368]
	Black-Black	Mismatched-Black	NS [HR: 1.056 (95% CI 0.999–1.116), p=.056]
Opelz et al 1977 [25a]	N/A	N/A	Statistical association described as being independent of recipient’s race
Perdue & Terasaki 1982 [26a]	White-White	White-Black	Patient survival rates “were essentially the same” (NS) but rates for the White-Black D/R pairing were “somewhat lower” than rates for White recipients. No p values reported

D/R – donor-recipient; HR – hazard ratio; NS – not significant; RR – risk ratio.

^aCaveat: Study did not specify if patient population included pediatrics.

Discussion

With nearly 90 000 patients on the U.S. kidney transplant waitlist and an ongoing shortage of donor organs, efforts to use donor organs more effectively and prolong graft survival remain a focal point of care [17,29]. To that end, the present systematic review examined the association between donor-recipient race-matching and graft and patient survival among Black and White kidney transplant recipients. We hypothesized the findings of this systematic review would demonstrate race-matching is not significantly associated with graft or patient survival. Consistent with our hypothesis, the studies in our systematic review generally indicated no significant differences in patient survival based on race-matching or mismatching, supporting that race-matching, on its face, has limited utility in patient survival.

Inconsistent with our hypothesis, the preponderance of studies (5 of 7) indicated that Black-Black, Black-White, and/or White-Black donor-recipient pairings were at greater risk for decreased graft survival. However, the findings are likely clinically insignificant, as GRADE suggests low-certainty evidence. This assessment was based on study design, with all 7 included studies being observational or case-control, as well as having a lack of factors that would increase certainty, such as large magnitude of effects. Observational studies are considered low-certainty evidence, due to increased risk of bias (eg, confounding) and inability to make causal inferences. Indeed, only 2 studies controlled for confounding factors, and closer examination of these 2 studies reveals their findings, although statistically significant, are of small magnitude. For example, LeClaire et al [2] found race-matched Black kidney transplant recipients experienced statistically significantly worse graft survival (ranging from 0.8% to 4%, depending on time period), compared with mismatched Black recipients, but concluded race-matching did “not influence patient outcomes enough to factor into organ allocation offers.”

The lack of large effects, low certainty of evidence, and insubstantial value in clinical practice noted in our systematic review supports the recent decision to remove the Black race coefficient from the KDPI [11,12]. The use of race as a coefficient in the KDPI scores a kidney from a Black donor as lower quality than from a non-Black donor [30,31]. Iltis [32] argued that this downgrading of Black donor kidneys contributed to increased non-use and potential waste of donor organs. Based on our findings, and to increase transplant access, we concur the quality of the current evidence does not justify utilization of a Black race coefficient to reduce the score of donor kidneys. Race is a social construct, rather than a biological one, and could be a likely proxy of genetic risk factors such as APOL1 gene variants and other factors (eg, the social determinants of health [SDOH) contributing to individual health [32–34]. As such, there is a strong argument for carefully considering how race is used in medical decision-making.

Additionally, strategies to improve organ allocation and transplant outcomes should focus on the SDOH, which are more salient factors underlying associations between race and health outcomes [34]. The SDOH are “conditions in the environment where people are born, live, learn, work, play, worship, and age that affect a wide range of health, functioning, and quality-of-life outcomes and risks” [35]. We posit kidney transplant access and outcomes may be bolstered through increased understanding of and intervening to address SDOH that negatively impact the health and well-being of some potential kidney transplant recipients and society as a whole (ie, the pool of potential kidney transplant donors). SDOH include the domains of healthcare access and quality, education access and quality, neighborhood and built environment, social and community context, and economic stability [35]. Donors can be affected by SDOH such as health insurance, food and housing insecurity, social support, employment, income, and health literacy in a number of ways that contribute to healthcare access, overall health and well-being, and ultimately, the viability of donor organs. These same SDOH can likewise affect the health and well-being of kidney transplant recipients, both before and after transplant, influencing the prevalence of chronic kidney disease and end-stage renal disease, access to pre- and post-transplant care (including immunosuppressant medications), and graft and patient survival outcomes.

Numerous approaches can be used to mitigate SDOH in kidney transplant care. One such approach starts with screening and monitoring SDOH, as identification of SDOH uniquely affecting individual patients will allow providers to recommend and coordinate with appropriate support services [36]. For example, kidney transplant recipients with limited income as a barrier to obtaining prescription medication can be referred to programs that specialize in supporting medication accessibility. Increasing access can, in turn, increase medication adherence, which is critical to graft survival. As another example, at the community level, Callendar et al [6] recommend health education campaigns raising awareness about the importance of organ health, which could serve 2 functions: encourage prevention of kidney disease and increase interest in and ability to serve as an organ donor. Future studies should evaluate the effects of SDOH-targeted interventions in improving kidney transplant care access and outcomes.

This systematic review has strengths and limitations. Among its strengths, the study used an expansive literature search strategy to capture studies that may otherwise have not been included in a more narrow strategy. Additionally, although studies with pediatric patients were excluded to eliminate this confounding factor, some studies were not explicit on this characteristic when describing their population; given this uncertainty and to optimize study inclusion yield, we elected to retain these studies in our synthesis. As the included studies were observational and retrospective in nature, causality of the relationship between race-matching and graft and patient survival outcomes cannot be determined. Although not a limitation, a meta-analysis was not conducted due to heterogeneity of the included studies.

Conclusions

This systematic review is the first of its kind to summarize evidence concerning the effects of donor-recipient race-matching on kidney transplant outcomes among Black and White recipients. Regarding patient survival, studies examining this outcome generally did not find significant differences based on race-matching. Although Black-Black, Black-White, and White-Black donor-recipient pairings were associated with decreased graft survival across some studies, because of their small magnitude, these effects are likely clinically irrelevant. As such, race-matching or mismatching between donor and recipient should not influence decision-making regarding organ allocation. Further investigation of donor and recipient factors affecting graft and patient survival, particularly genetic and structural factors influencing health, is warranted to improve utilization of donor kidneys, access to kidney transplantation, and outcomes of kidney transplant recipients.