Skip to main content
Premium Trial:

Request an Annual Quote

CAP Survey Sees Labs Aware of New Kidney Function Equations Aimed at Reducing Racial Disparities


NEW YORK A survey conducted by the College of American Pathologists indicates that a majority of clinical laboratories are aware of recent changes to kidney function estimation equations designed to eliminate racial disparities in care but that implementation of the new equations lags behind this awareness.

According to the survey, which was published Tuesday in the Journal of the American Medical Association, around 75 percent of labs queried were aware of the new equations, which were published in 2021. Only around 30 percent of the surveyed labs have adopted the new equations, however, and of the roughly 70 percent who have not adopted them, more than half said that they were unsure when they would put them into practice.

The new equations remove Black race as a factor from estimations of glomerular filtration rate, a standard measure of kidney function. Typically, estimated glomerular filtration rate (eGFR) has been calculated using patients' serum creatinine levels along with factors including age, gender, and whether or not a person was Black.

Being Black has been included in certain widely used eGFR equations due to observations in previous studies that Black individuals had higher average measured GFR (which measures how quickly patients clear certain exogenous analytes and is considered a gold standard of kidney function measurement) than did non-Black individuals with the same age, sex, and serum creatinine measurements. This observation suggested that eGFR equations based solely on those three factors might underestimate the kidney function of Black individuals, which could, for instance, lead to Black patients being unnecessarily flagged as being at risk of kidney disease or being made ineligible for certain medical treatments or heightened drug doses due to concerns about kidney function.

Inclusion of race in eGFR equations was meant to address these concerns. However, clinicians have raised concerns about inclusion of this so-called racial coefficient, noting that, among other things, it is based on a small number of small studies and that it may lead clinicians to overestimate the kidney function of their Black patients, which could lead to delayed diagnoses and care.

The new equations remove race from the factors used to calculate eGFR and include the option to add cystatin C as a measurement. In a New England Journal of Medicine paper published last year introducing the new equations, the authors found that the new equation comprised of age, sex, and serum creatinine underestimated measured GFR in Blacks and overestimated it in non-Blacks, which consequently "increased estimates of [chronic kidney disease] prevalence among Blacks and yielded similar or lower prevalence among non-Blacks."

They also noted that the new equation including cystatin C in addition to creatinine was more accurate than the creatinine-only equation and showed smaller differences between Black and non-Black individuals. In the case of all equations, 85 percent of eGFRs for Black and non-Black patients were within 30 percent of their measured GFRs.

Jonathan Genzen, professor of clinical pathology at the University of Utah, chief medical officer at ARUP Laboratories, and chair of CAP's clinical chemistry committee, said that CAP has made driving awareness of the new eGFR equations a priority.

"We're committed to an awareness campaign to make sure that laboratories know about this and that they are moving forward appropriately," he said.

Genzen noted that while a majority of surveyed labs have not yet implemented the new equations, the roughly 30 percent adoption rate is relatively good for a guideline that at the time of the survey had only been out for several months.

"I would say it is much faster than adoption of many prior eGFR equations in the past," he said. "We have really tried to have a united voice in advocating for this, just to create some inertia around the priority, just so that labs when they are talking to their internal teams know how to prioritize it appropriately."

Genzen cited a number of factors that could delay labs in moving over to the new equations, among them the need to validate the new equations in their facilities and the need to implement them within their lab information and EHR systems. Large reference labs, he said, may need time to communicate with their customer labs so that they can make needed changes to their systems.

Coordination with clinicians can also add to the time required to shift to the new equations, Genzen said.

"You certainly don't want to surprise anybody with changes," he said. "At many institutions it requires clinician education and approval from the medical advisory board of the hospital or health system so that everybody is on board with the change and so that you have clarity on what the new equation is, when the change will occur, and what impact the change will have on different populations."

Adoption of the more accurate equation that includes cystatin C remains well behind that of the new equation that does not include that marker. In the survey, less than 3 percent of respondents said they had adopted the cystatin C equation, while roughly 10 percent of respondents said they planned to adopt it. More than 30 percent said they did not plan to adopt this version of the equation, and more than half said that they were unsure if they would adopt it.

When asked about barriers to including cystatin C, more than half of the labs cited limited options for testing, while around a quarter cited the cost of the test. Roughly a quarter of labs also highlighted a lack of staff to implement cystatin C testing.

Genzen noted that while creatinine is an inexpensive and commonly performed lab test that is included in basic metabolic panels, cystatin C is more expensive and isn't typically included in such panels. He said that the CAP initiative aimed to promote better availability of cystatin C testing "because it does perform better when you include cystatin C along with creatinine in the new equations."

He added, though, that cystatin C might add the most value in cases where patients have already been referred to a nephrologist due to suspicion of kidney disease.

"It may not be necessary in the broad, general screening of the whole population, which is essentially what you are getting with creatinine," he said.

He added that he expected that, driven in part by the new eGFR equations, over time more options for cystatin C testing on common lab instruments will come to market, improving pricing and access to the test.

"It's a transition that is happening, but it is nowhere near as widespread as creatinine," he said.