The role of comorbidities and insurance type in explaining intersectional racial and gender disparities in kidney transplant waitlisting: A mediation analysis

Background: Kidney transplantation is lifesaving treatment for patients with kidney failure, yet Black patients and women are less likely to be waitlisted for transplant compared to White patients and men, respectively. Combined (i.e., intersectional) disparities are likely particularly large, yet research examining combined racial and gender disparities in waitlisting is lacking and has not investigated potential underlying mechanisms. This study aimed to quantify the role of insurance type – an indicator of care access and socioeconomic status – and comorbidities in driving intersectional disparities in kidney transplant waitlisting in the United States (US).
Methods: We used the US Renal Data System, a national registry, to conduct a retrospective cohort study of all non-Hispanic Black and non-Hispanic White adults (≥ 18 years old) initiating kidney replacement therapy (KRT; dialysis or transplantation) from 2015-2019, with follow-up through 2021. We fit age-adjusted Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for racial and gender disparities in time from KRT initiation to waitlisting. We conducted mediation analysis using inverse odds ratio weighting to estimate the percentage of the disparity explained by comorbidities (including cardiac disease, hypertension, diabetes, cancer, and obesity) and insurance. We considered insurance type before and after KRT initiation separately, given KRT-related changes in public insurance eligibility. We also stratified analyses of pre-KRT insurance by age, given changes in public insurance eligibility at age 65.
Results: Among 440,065 patients initiating KRT (32% Black, 42% women), 16% were waitlisted. Disparities by race and gender ranged from 16% to 38%, with the largest gap between Black women and White men (Table 1).

In general, comorbidities explained less than 10% of the disparities between race-gender groups. Negative estimates for percentage mediated for some conditions (such as cardiac disease, peripheral vascular disease, and cancer), indicated that these conditions offset rather than increase disparities, particularly gender disparities among Black adults. Pre-KRT insurance explained approximately a quarter of the disparities overall, driven by strong mediating effects (32-37%) among patients under 65 years old, with no substantial mediating effect among those 65 and older. Comorbidities and insurance together explained approximately 20% of the racial disparity, 40% of the gender disparity, and 25% of the disparity between Black women and White men (Figure 1). 

Conclusion: Insurance type contributes more to racial and gender disparities in waitlisting than does comorbidity burden. However, the majority of the disparities remain unexplained, indicating the need for future research to investigate the role of other non-medical factors, such as income, education, employment, and access to transportation.