New Equations to Estimate GFR in Children with CKD

TLDR

The Schwartz formula, developed in the 1970s, now overestimates glomerular filtration rate in children due to changes in creatinine measurement methods, highlighting the need for updated equations. This study aimed to develop new GFR‑estimating equations for children with chronic kidney disease using baseline data from 349 participants in the CKiD cohort. Linear regression analyses incorporating height, serum creatinine, cystatin C, blood urea nitrogen, and gender were used to construct the improved formula. Median iohexol‑GFR was 41.3 ml/min/1.73 m² with serum creatinine 1.3 mg/dl, and the newly derived equation achieved 87.7 % of estimates within 30 % of measured GFR, outperforming prior pediatric formulas and enabling a simple bedside approximation of 0.413 × (height/serum creatinine).

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 m(2) (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 m(2))=39.1[height (m)/Scr (mg/dl)](0.516) x [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.