Timed-urine collections for renal clearance studies

Area of Science:

• Nephrology
• Pediatric Nephrology
• Clinical Chemistry

Background:

• Accurate measurement of renal function is crucial in pediatric and adult patients.
• Timed-urine collections are standard for renal clearance studies, but their reproducibility can impact results.
• Glomerular filtration rate (GFR) is a key indicator of kidney function.

Purpose of the Study:

• To assess the reproducibility of timed-urine collections in pediatric renal clearance studies.
• To determine the impact of urine collection variability on glomerular filtration rate (GFR) measurements.

Main Methods:

• Analysis of 222 cimetidine clearance studies (GFR-Cim) from 32 pediatric patients over 8 years.
• Measurement of urinary creatinine excretion rates during supervised urine collection periods.
• Comparison of creatinine excretion rates within each child to evaluate urine collection reproducibility.

Main Results:

• The coefficient of variation (CV) for creatinine excretion rate was approximately 10% in both children and adults.
• The expected CV for GFR during repeated renal clearance studies using voided urine collections was 12% to 14% in both pediatric and adult subjects with stable GFR.

Conclusions:

• Timed-urine collections demonstrate acceptable reproducibility for renal clearance studies.
• Variability in urine collection contributes a CV of 12-14% to GFR measurements, a consistent finding across pediatric and adult populations.
• These findings support the reliability of timed-urine collections for assessing GFR in clinical settings.