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 4.8 years to 21 years at the time of a study. The urinary creatinine excretion rate is measured during supervised urine collection periods. The creatinine excretion rates in each child were compared to obtain data on the reproducibility of the urine collections. The coefficient of variation (CV) of the creatinine excretion rate is approximately 10% in both children and adults. The variation in GFR to be expected during repeated renal clearance studies in subjects with stable GFR, using voided urine collections, was similar in children and adults, with a CV of 12% to 14%.