Received March 12, 2008
Accepted on August 26, 2008

CLINICAL EPIDEMIOLOGY

New Equations to Estimate GFR in Children with CKD

George J. Schwartz ^*1, Alvaro Muñoz , Michael F. Schneider , Robert H. Mak , Frederick Kaskel , Bradley A. Warady ^||, and Susan L. Furth ^¶

*Department of Pediatrics, University of Rochester School of Medicine, Rochester, and Department of Pediatrics, Albert Einstein College of Medicine, Bronx, New York; Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health and ¶Department of Pediatrics, Johns Hopkins School of Medicine, Baltimore, Maryland; Department of Pediatrics, Children’s Hospital of San Diego, San Diego, California; ||Department of Pediatrics, Children’s Mercy Hospital, Kansas City, Missouri

¹ To whom correspondence should be addressed. E-mail: george_schwartz{at}urmc.rochester.edu.

	Abstract

The Schwartz formula was devised in the mid-1970s to estimate GFR in children. Recent data suggest that this formula currently overestimates GFR as measured by plasma disappearance of iohexol, likely a result of a change in methods used to measure creatinine. Here, we developed equations to estimate GFR using data from the baseline visits of 349 children (aged 1 to 16 yr) in the Chronic Kidney Disease in Children (CKiD) cohort. Median iohexol-GFR (iGFR) was 41.3 ml/min per 1.73 m² (interquartile range 32.0 to 51.7), and median serum creatinine was 1.3 mg/dl. We performed linear regression analyses assessing precision, goodness of fit, and accuracy to develop improvements in the GFR estimating formula, which was based on height, serum creatinine, cystatin C, blood urea nitrogen, and gender. The best equation was

GFR(ml/min per 1.73 m²)=39.1[height (m)/Scr (mg/dl)]^0.516x[1.8/cystatin C (mg/L)]^0.294[30/BUN (mg/dl)]^0.169[1.099]^male[height (m)/1.4]^0.188.

This formula yielded 87.7% of estimated GFR within 30% of the iGFR, and 45.6% within 10%. In a test set of 168 CKiD patients at 1 yr of follow-up, this formula compared favorably with previously published estimating equations for children. Furthermore, with height measured in cm, a bedside calculation of 0.413*(height/serum creatinine), provides a good approximation to the estimated GFR formula. Additional studies of children with higher GFR are needed to validate these formulas for use in screening all children for CKD.