After reassessing the inclusion of race in an equation used to estimate kidney function—a practice that has come under increased scrutiny—a joint task force of the National Kidney Foundation (NKF) and American Society of Nephrology (ASN) is recommending using a new equation that doesn’t involve a race variable to gauge kidney function.
The report has been published in both the NKF’s American Journal of Kidney Diseases and the ASN’s Journal of the American Society of Nephrology.
In recent years, use of an equation that incorporates race for estimating kidney function (the estimated glomerular filtration rate, eGFR) has been undergoing reassessment in light of criticism that race is an inadequate proxy for genetic differences. Furthermore, the equation assigns a higher eGFR to Black patients, and some critics also have argued that equations for estimating kidney function that include race as a variable “unduly restrict access to care in some cases, yet offer only modest benefits to precision.”
Measuring the GFR is a complex process that is rarely performed outside of research settings. Instead, equations to estimate kidney function have been in use for nearly 50 years, based on blood levels of creatinine (a breakdown product of muscle that is a marker for kidney function) and other factors, such as weight, age, and sex. An interim report by the task force notes that for nearly 2 decades, equations have included a “race” variable (Black or non-Black), prompted by studies indicating that average levels of creatinine are higher in Black patients compared with White patients.
Including the race variable, which increases the eGFR in Black patients by 16% (indicating a comparatively higher level of kidney health), was intended to provide more accurate estimates of kidney function. But there are concerns that use of race in eGFR calculation has the potential to underestimate the severity of illness in Black patients and delay their access to kidney transplantation. Being wait-listed for a kidney transplant in the United States is based on a specific eGFR threshold, and the race variable means that a White patient just below that threshold would qualify for wait-listing, whereas a Black patient with the same creatinine level would not.
“Given considerable evidence of disparities in health and healthcare delivery in African American communities, some regard keeping a race term in GFR equations as a practice that differentially influences access to care and kidney transplantation,” the task force report says.
Some medical institutions have already acted to eliminate race in eGFR equations, spurred by efforts of concerned medical students, residents, fellows, and trainees. These include Beth Israel Deaconess Medical Center, which discarded race from reporting of eGFR in laboratory reports in 2017, as well as the University of Washington health system, Vanderbilt University Medical Center, and other centers.
The NKF and the ASN established the task force in 2020 to reassess the inclusion of race in estimating GFR and its implication for diagnosis and treatment of patients with or at risk for kidney disease. The group deliberated for 10 months and considered 26 approaches for estimating GFR, narrowing the list down to 5 for a closer look.
The task force is now recommending that laboratories and clinicians immediately implement a revised or “refit” equation that eliminates the race variable, called the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation, which was developed based on data from a large, diverse pool of patients.
“The NKF and ASN urge all laboratories and healthcare systems nationwide to adopt this new approach as rapidly as possible so that we can move towards a consistent method of diagnosing kidney diseases that is independent of race,” said NKF President Paul M. Palevsky, MD, in a joint statement with ASN President Susan E. Quaggin, MD. Recommending the CKD-EPI creatinine equation refit without the race variable is “promoting health care justice,” she said.
Two separate studies, issued on the same day as the task force report, show that incorporating a biomarker of kidney function called cystatin C in equations estimating kidney function improves accuracy.
One report, by the CKD-EPI group, showed that newly developed eGFR equations that exclude race but include measures of both creatinine and cystatin C were more accurate and led to smaller differences between the estimated GFR and measured GFR than new equations that omit the race variable but include only creatinine or cystatin C.
The second report had similar findings, showing that compared with equations using creatinine alone, equations that include cystatin C resulted in smaller differences between eGFR and measured GFR. It also showed that excluding race did not affect the equations’ predictive ability.
The task force’s recommendation to use the new “refit” CKD-EPI creatinine equation doesn’t include use of cystatin C. Unlike creatinine, cystatin C is not routinely used as a marker in evaluating kidney function, because most US clinical laboratories do not perform cystatin C tests and it is more costly.
However, the task force made a second recommendation, calling for “national efforts to facilitate increased, routine, and timely use of cystatin C, especially to confirm eGFR in adults who are at risk for or have chronic kidney disease, because combining filtration markers (creatinine and cystatin C) is more accurate and would support better clinical decisions than either one marker alone.”
The report notes that if evidence demonstrates acceptable performance of approaches to estimate kidney function that include cystatin C and omit the race variable, they “should be adopted to provide another first line test in addition to confirmatory testing.”
Published: October 5, 2021. doi:10.1001/jamahealthforum.2021.3788
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Stephenson J. JAMA Health Forum.
Corresponding Author: Joan Stephenson, PhD, Consulting Editor, JAMA Health Forum (Joan.Stephenson@jamanetwork.org).
Conflict of Interest Disclosures: Dr Stephenson reported receiving payment for editorial work for the Journal of the American Society of Nephrology.
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Stephenson J. Task Force Advises Excluding Race as Factor in Estimates of Kidney Function. JAMA Health Forum. 2021;2(10):e213788. doi:10.1001/jamahealthforum.2021.3788