Timed-urine collections for renal clearance studies.

The purpose of this study was to describe the reproducibility of timed-urine collections for renal clearance studies and the effect variations in urine collection has on measurement of glomerular filtration rate (GFR). Data from 222 cimetidine clearance studies (GFR-Cim) were obtained from 32 pediatric renal patients over a period of 8 years. There were three to 18 studies per child aged 4.

Measurement of renal functional reserve in children.

Renal functional reserve was measured during 89 studies in 78 children as the difference between the baseline glomerular filtration rate (GFR) and that following a protein meal. GFR was measured using creatinine as the filtration marker in children pre-treated with cimetidine. The children had been on a diet free of meat, fish, and fowl for 24 h.

Comparison of two formulae for estimation of glomerular filtration rate in children.

Glomerular filtration rate (GFR) was measured in 216 studies in 151 children using the cimetidine protocol. This was compared with the GFR calculated using Léger's pharmacokinetic equation and with that calculated using k*L/[Cr](s )(constant x length in centimeters divided by serum creatinine concentration). The GFR calculated using the equation GFR=k*L/[Cr](s) yielded a closer approximation to the measured GFR than that using Léger's pharmacokinetic equation.

The ratio of urinary cystatin C to urinary creatinine for detecting decreased GFR.

Glomerular filtration rate (GFR) and urine and serum concentrations of cystatin C and creatinine were measured in 40 boys and 42 girls. The fractional excretion of cystatin C (FE Cyst C) increased in proportion to the decrease in GFR. Since serum creatinine concentration (S-Creatinine) in the numerator of the fractional excretion equation and serum cystatin C concentration (S-Cystatin C) in the denominator have similar numerical values, they cancel out.