[Evaluation of the applicability of three prediction equations for estimating glomerular filtration rate in children with chronic kidney disease].

Objective: Accurate and reliable assessment of renal function is important in the management of children with chronic kidney disease (CKD). Glomerular filtration rate (GFR) is the best index of assessing kidney function. For assessment of GFR, both gold standard tests and prediction equations have been used. The well-known 24-hour endogenous creatinine clearance (Ccr), the Schwartz formula and the Filler formula are increasingly used in daily clinical practice. However, there are few studies on the applicability of these prediction equations for estimating GFR in Chinese children with CKD. The aim of this study was to compare these prediction equations estimating GFR with an isotope clearance method [isotope glomerular filtration rate (rGFR)] in such patients.

Method: Children aged 1-16 years who underwent isotope (99m)Tc-diethylenetriaminepentaacetic acid ((99m)Tc-DTPA) GFR testing (Gates' method) between the year of 2002 and 2005 were studied retrospectively. GFR was estimated using: (1) 24-hour Ccr, which was calculated using the standard formula: [urine creatinine (milligrammes per millilitre) × 24-hour urine volume/serum creatinine (milligrammes per millilitre) × 1440] × [1.73 (m(2))/body surface area (m(2))]; (2) the Schwartz formula, which is: eGFR (ml/min per 1.73 m(2)) = k × height (centimetres)/serum creatinine (micromoles per litre), where k is 62 in males at 13 years of age and older, 40 in infants, and 49 in all other children; and (3) the Filler formula, which is: logGFR = 1.962 + [1.123 × log(1/Cys C)], where cystatin C is measured in milligrammes per litre. Serum and urinary creatinine levels were detected by alkaline kinetic method. Serum cystatin C was analysed by particle-enhanced immunoturbidimetric assay. Bias and precision were evaluated.

Result: Thirty subjects (18 males and 12 females; mean age 9.4 years) fulfilling both inclusion criteria and exclusion criteria were included in this study. The mean (SD) rGFR was 81.57 (36.92) ml/min per 1.73 m(2); 18 subjects were in CKD stage I, 8 in CKD stage II, 8 in CKD stage III, and 1 in CKD stage IV. Only the mean 24 h Ccr-eGFR was slightly higher than rGFR (0.4 ml/min per 1.73 m(2) higher). Within 95% limits of agreement, the maximum absolute value of bias was about 50 ml/min per 1.73 m(2). Accuracy (estimated GFR values within ± 30% of rGFR) for all formulae was poor, ranging from 23.3% to 43.3%. All formulae overestimate or underestimate rGFR in different CKD stages.

Conclusion: In Chinese children with CKD, there was a significant difference between measured GFR and estimated GFR using 24h Ccr, Schwartz formula and Filler formula. More suitable GFR predictive equations to assess glomerular function of such patients should be developed.