New Equation Provides Better Estimates of CKD Prevalence

A newly developed equation provides more accurate estimates of glomerular filtration rate (GFR) than do other measures, according to new research. The equation is different from other measures because it was developed on the basis of findings from pooled databases, rather than from a single study.

“Our new estimating equation, developed from pooled databases, is more accurate than the widely used Modification of Diet in Renal Disease (MDRD) Study equation,” said Andrew S. Levey, MD, of Tufts Medical Center, one of the study authors and a participant in the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI).

The MDRD Study equation, developed from data on approximately 1600 patients in a single study, uses information on age, race, sex, and the level of serum creatinine to estimate GFR. The equation is relatively imprecise and can underestimate GFR, especially at levels that are closer to normal, or higher. As a result, clinical laboratories do not generally report estimated GFR (eGFR) levels greater than or equal to 60 mL/min/1.73 m2.

Measurement of GFR is impractical for routine clinical use. To help improve GFR estimation, the researchers developed a new equation based on pooled databases, initially using data on more than 8000 patients from 10 studies. They then validated the equation by using data on 3896 patients from 16 studies.

The resulting CKD-EPI equation was more accurate than the MDRD Study equation, especially at higher levels of kidney function, when compared against actual GFR measurements. More accurate eGFR is likely to reduce the frequency of false-positive diagnosis of CKD and to refine the classification by stage in patients with CKD.

When applied to a representative sample of 16,000 Americans, the CKD-EPI equation yielded an estimated prevalence of CKD in the general population of 12.2 percent; CKD prevalence estimated with the MDRD equation was 13.3 percent. Among those with CKD, the proportion with stage 1 and 2 CKD was 17 percent and 21 percent, respectively, with the CKD-EPI equation, versus 13 percent and 24 percent, respectively, with the MDRD Study equation.

The investigators suggested that the CKD-EPI equation could replace the MDRD Study equation. They cautioned that GFR estimates are not as accurate as GFR measurements and that the CKD-EPI equation may not be accurate for all populations of patients.

The study, “A New Equation to Estimate GFR from Serum Creatinine Improved Accuracy and Updated Estimates of Prevalence of Chronic Kidney Disease in the United States,” was part of the Renal Week session on “Effects of Traditional and Nontraditional Risk Factors on Cardiovascular Risk in Chronic Kidney Disease and End Stage Renal Disease.”