A race-free revision of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation for calculating estimated glomerular filtration rate (eGFR), introduced in September 2021, has rapidly penetrated US practice.
By March 2022, 30% of US clinical laboratories that responded to a survey said that they were using the new race-free eGFR equation, including 35% of nonhospital laboratories (which includes commercial laboratories) and 32% of laboratories at academic hospitals and medical centers, according to a recently published survey report in the Journal of the American Medical Association (JAMA).
To put this rate of uptake into perspective, the last time nephrologists asked US laboratories to change the eGFR equation — the 2009 introduction of the original CKD-EPI equation — a scant 25% of US laboratories had adopted the CKD-EPI equation roughly a decade later, according to a 2018 report by the College of American Pathologists (CAP).
Both the original 2009 CKD-EPI equation for calculating eGFR and its predecessor equation introduced in 1999, the MDRD equation, included an adjustment factor that raised the eGFR value if a person self-identified as Black.
Controversy over this scientifically questionable adjustment bubbled within the nephrology community for several years and eventually led to formation of a task force by the National Kidney Foundation and the American Society of Nephrology that resulted in the task force's 2021 report, which recommended US laboratories switch to the race-free version of the CKD-EPI equation.
A "Very Early" Look at Uptake
"This was the first somewhat systematic survey" to track adoption of the 2021 race-free CKD-EPI equation for eGFR, and it took place "very early in the implementation process," commented Paul M. Palevsky, MD, a nephrologist who is the immediate past-president of the National Kidney Foundation and had no role in the survey or data analysis.
The survey was conducted in March 2022 and, given that several actions remained to be taken at that time to fully pave the path to widespread adoption of the revised equation, the finding that roughly a third of laboratories had already begun using the new equation at that time is "remarkable," Palevsky said in an interview.
"To have this level of uptake within 6 months of online publication is really quite good," added Palevsky, a professor at the University of Pittsburgh School of Medicine, Pennsylvania, and deputy executive director of the US Department of Veterans Affairs (VA) Kidney Medicine Program.
Adoption Gains Momentum
CAP distributed their March 2022 survey to 6317 clinical laboratories that had participated in CAP's first 2022 general-chemistry proficiency testing survey and received usable responses from 4298 laboratories (68%), and 87% of responding laboratories were located in the United States.
Analysis of the survey results, run by researchers from several US academic and commercial clinical laboratories as well as a CAP representative, focused exclusively on responses from US-based laboratories.
Several additional steps taken since March will likely have substantially broadened adoption of the race-free equation, Palevsky said. These include:
A January 2022 directive from the VA required all its locations to use the race-free equation starting by April 1, 2022. According to Palevsky, at least 131 of the VA's 171 laboratories had certified their change-over by then.
The Board of Directors of the Organ Procurement and Transplantation Network unanimously approved a measure in June 2022 that required transplant hospitals to use a race-neutral calculation when estimating a patient's level of kidney function prior to listing for a kidney transplant, effective July 27, 2022.
Adoption of the race-free equation by Quest Diagnostics in July 2022, a commercial laboratory that ran about 66 million serum creatinine tests in 2021 (serum creatinine is the measure at the core of calculating eGFR). This followed adoption of the equation by the other major US commercial lab, LabCorp, at the end of February 2022, a company that ran about 51 million serum creatinine tests in 2021, said Palevsky. He estimated that US practice involves about 250 million total serum creatinine assays annually, so this change by the two largest-volume commercial laboratories affected more than 40% of the US test volume.
A representative of the Epic Cosmos database, which includes records for 167 million US patients and 247,000 US physicians, recently told Palevsky that 70% of recent laboratory reports for eGFR used the 2021 race-free CKD-EPI equation as of late October.
Preliminary findings to October 31, 2022, from a survey sent from the Association of Pathology Chairs to clinical laboratories at academic medical centers showed that among 68 completed surveys, 45 (66%) laboratories reported adoption of the 2021 race-free CKD-EPI equation.
Cystatin C Use Still Lags
The March 2022 numbers from the CAP survey show a different picture for use of serum cystatin C as a complement to serum creatinine when calculating eGFR without adjustment by race.
The September 2021 report by the task force organized by the National Kidney Foundation and the American Society of Nephrology that endorsed adoption of the race-free equation also included a recommendation for "increased, routine, and timely use of cystatin C, especially to confirm eGFR in adults who are at risk for or have CKD. Combining filtration markers (creatinine and cystatin C) is more accurate and would support better clinical decisions than either marker alone," the task force wrote.
Despite this, the survey numbers from March 2022 in the recent JAMA report document an ongoing low rate of attention paid to cystatin C. The survey showed that 8.0% of responding US laboratories planned to include cystatin C when reporting eGFR values.
The most common reasons for this low use, the laboratories said, were limited cystatin C testing options (cited by 58%), the added cost for cystatin C testing (cited by 23%), and staff resource issues (also cited by 23%) (laboratories could cite more than one barrier).
"We knew that increasing cystatin C testing would be a tougher hill to climb," admitted Palevsky. Any effort to boost availability of this measure starts from a deep existing hole. Of the roughly 6000 US clinical laboratories, fewer than 200 have provided cystatin C testing. And 2018 data from Medicare showed that compared with 39 million orders for serum creatinine testing, the cystatin C tally was around 110,000, about 0.3% of the creatinine test volume.
For the time being, the focus of the National Kidney Foundation is working with the American Society of Nephrology and other organizations including the American Association for Clinical Chemistry to promote the race-free eGFR equation based on serum creatinine levels, Palevsky said.
"Cystatin C testing is a secondary issue. The primary task is getting the new, race-free eGFR equation implemented."
The CAP survey received no commercial funding. Palevsky has reported no relevant financial relationships.
JAMA. 2022;328:2060-2062. Abstract
Mitchel L. Zoler is a reporter for Medscape and MDedge based in the Philadelphia area. @mitchelzoler
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Cite this: Race-Free eGFR Equation for Kidney Function Adopted Quickly in US - Medscape - Dec 02, 2022.