Monitoring renal function in children with urological abnormalities

In clinical practice glomerular filtration rate routinely is estimated by measuring serum creatinine and using the Schwartz formula for calculating an estimate of creatinine clearance or using the Gates formula for calculating the clearance of diethylenetriaminepentaacetic acid based on the uptake during radionuclide imaging. We compared these methods to the plasma clearance of iothalamate during extended constant infusion. All 3 tests were performed in 14 boys and 5 girls 9 months to 16 years old with urological abnormalities and moderate renal insufficiency. Using iothalamate as the reference, calculated creatinine clearance overestimated glomerular filtration rate by more than 20% in 12 of the 19 patients (63%). Diethylenetriaminepentaacetic acid uptake grossly overestimated glomerular filtration rate; in only 3 instances was the estimate within 20%. The accuracy of both formulas was better in older patients and in those with more normal renal function. We conclude that the Gates formula for measuring glomerular filtration rate is grossly inaccurate in children with diminished renal function and the Schwartz formula, although better, has a poor level of predictability.