Use of conventional race-modified equations contributes to potential overestimated renal function and may account for part of the observed lower use of nephron-sparing surgical approaches in Black patients, find Cleveland Clinic researchers in a study published recently in JU Open Plus. The retrospective review of over 6,000 patients who underwent partial (PN) or radical nephrectomy (RN) at Cleveland Clinic found that the disparity was most pronounced in Black patients with estimated normal kidney function.
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“It’s well known that disparities exist in the use of partial nephrectomy in Black patients in the U.S., even though on average, Black patients have a higher risk of chronic kidney disease [CKD] and high blood pressure and of needing dialysis,” says Christopher Weight, MD, Director of Cleveland Clinic’s Center for Urologic Oncology and lead author of the study. “So why are we not taking surgical approaches that preserve renal function in this patient cohort?”
Race-modified equations were originally designed to account for the higher average muscle mass of a Black patient, because kidney function is closely tied to clearance of creatine, which is a breakdown product from muscle. A similar modification still exists for sex differences, but their use with race, has been questioned recently and ultimately recommended for discontinuation. “Assumptions about biology based on a social construct like race are tricky and potentially harmful, and so we wanted to evaluate the role these equations may play and the effect of the new equations on estimating chronic kidney disease risk,” adds Dr. Weight.
Research suggests that nephron-sparing approaches to renal cell carcinoma like PN are associated with lower overall mortality and risk of developing CKD, and PN is the standard care for clinical T1a lesions, according to American Urological Association (AUA) Renal Mass and Localized Renal Cancer Guidelines. But Black patients undergo RN more often and have lower transplantation rates and longer transplantation waits than non-Black patients, despite the established higher risk of CKD. The research team sought to discover whether race-modified equations contribute to this disparity.
Measuring the impact of race-modified and race-free equations
Researchers reviewed 6,327 patients who self-reported their race before undergoing PN (N = 3,533) or RN (N = 2794). Just over 10% of patients were Black. Researchers controlled for known factors associated with PN and then analyzed the impact of race-modified and race-free equations on the distribution of patients across CKD stages. They found that when compared with non-Black patients, Black patients had higher comorbidity rates and lower preoperative estimated glomerular filtration rate (eGFR) (P < 0.001) as well as lower overall PN rates (49% vs. 57%; P < 0.001). The disparity in overall PN rates was most pronounced in the CKD stage 1 group (55.84% vs. 67.43%; P = 0.0011). Ultimately, when controlling for known confounders on multivariate logistic regression analysis, the study found the Black race to be associated with lower odds of receiving PN (OR = 0.76 (0.61-0.96), P = 0.001).
“We controlled for baseline kidney function, socioeconomic factors, tumor size and even complexity,” says Dr. Weight. “The disparity still persisted.”
The next step for researchers was to determine whether a simple switch to race-free equations for CKD staging would have an impact on this disparity. Many in the medical community have suggested abandoning race-modified equations due to the potential to perpetuate biases. Researchers in this study found that 27% of patients in the study would be reclassified to a worse CKD group when using the race-free (CDK-EPI-refit) equation.
“The race-modified equations appear to be overestimating a patient’s kidney function for Black patients, so when making a decision that balances cancer eradication and long-term kidney function, the team may lean toward cancer eradication with radical nephrectomy,” says Dr. Weight, “when really, in some of these patients, the kidney function is more precarious than presumed.”
Fortunately, notes Dr. Weight, the disparity was not apparent among patients in more severe CKD stages. “Our findings show that race-modified equations account for some but not all of the disparity in partial nephrectomy use. We need to keep searching for answers to ensure people of all races receive appropriate care.”