Cystatin C-based equation performs well for estimating GFR

The European Kidney Function Consortium cystatin C equation, which does not include race- or sex-specific factors, was more accurate than other common equations for predicting glomerular filtration rate (GFR), an international study found.

A cystatin C-based equation to estimate glomerular filtration rate (GFR) was more accurate than other commonly used equations, a new study found.

The European Kidney Function Consortium (EKFC) developed a creatinine-based equation (EKFC eGFRcr) to estimate glomerular filtration rate (GFR) with a rescaled serum creatinine level, meaning that the serum creatinine level is divided by the median serum creatinine level among healthy persons to control for variation related to differences in age, sex, or race. The same group used data from 227,643 patients in Sweden to estimate the rescaling factor for cystatin C level in adults and replaced serum creatinine in the EKFC eGFRcr equation with rescaled cystatin C, reasoning that cystatin C involves less non-GFR variation related to age, sex, and race. The resulting equation, the EKFC eGFRcys equation, was validated in cohorts of White patients and Black patients in Europe, the United States, and Africa (n=11,231, 1,093, and 508, respectively), according to measured GFR, levels of serum creatinine and cystatin C, age, and sex. The results were published Jan. 26 by the New England Journal of Medicine.

For the EKFC eGFRcys equation, the rescaling factor for cystatin C was estimated at 0.83 for men and women younger than age 50 years and at 0.83+0.005×(age−50) for those age 50 years and older. The new equation was unbiased, was similarly accurate versus the EKFC eGFRcr equation in both White and Black patients, and was more accurate than the Chronic Kidney Disease Epidemiology Collaboration's (CKD-EPI) cystatin C-based equation, which is recommended by Kidney Disease: Improving Global Outcomes (KDIGO). Using the arithmetic mean of both EKFC equations further improved the accuracy of estimated GFR over estimates from either equation alone.

The researchers noted that the methods used to measure GFR varied among the cohorts and that the validation cohorts did not include children or White and Black adults from the United States or Asia. “We found that a single mathematical equation (the EKFC equation) with serum creatinine could also be used with cystatin C to accurately estimate GFR,” the authors concluded. “The performance of the EKFC eGFRcys equation tested in this study was equivalent to that of the EKFC eGFRcr equation, and the EKFC eGFRcys equation had somewhat better accuracy than the 2021 CKD-EPI equations (refitted without the race coefficient) that have been the subject of recent reports.”

A feature article in the May 2021 ACP Internist discussed use of race in clinical algorithms, including those for GFR.