Mean of creatinine clearance and urea clearance examined over 1 h estimates glomerular filtration rate accurately and precisely in children.

Aim: Accurate and precise estimation of glomerular filtration rate (GFR) is essential in kidney disease. We evaluated the usefulness of the mean of creatinine clearance (CCr) and urea clearance (CUN) examined over a 1‐h urine collection period (1‐h (CCr + CUN)/2) in a retrospective, cross‐sectional study across two centres, as a relatively simple method for estimating GFR in children. Methods: Children aged ≤18 years who underwent inulin clearance (CIn) tests were eligible. Two clearance values were obtained during a 2‐h test consisting of two periods of 1 h each. The mean clearance in two periods was defined as 1‐h clearance. 1‐h (CCr + CUN)/2, 1‐h CCr, 1‐h CUN and GFR estimated by Cr‐based and cystatin C (CysC)‐based formulas for Japanese children were compared with CIn. Bland–Altman plots were used to evaluate correlations. The primary outcome measure was the correlation between 1‐h (CCr + CUN)/2 and CIn. Results: Fifty‐three children were analysed. Their median age was 10.9 (interquartile range [IQR] 5.3–14.2) years, and median CIn and 1‐h (CCr + CUN)/2 were 77.0 (IQR: 51.5–95.1) and 81.0 (IQR: 64.1–97.7) ml/min/1.73 m2, respectively. Percentage difference of CIn and 1‐h (CCr + CUN)/2 in the Bland–Altman plot was −11.2% (95% confidence interval − 15.3% – −7.1%), with 95% lower and upper limits of agreement of −40.3% and 18.0%, respectively. Thus, 1‐h (CCr + CUN)/2 was 1.12 times CIn. Conclusion: 1 h (CCr + CUN)/2 was almost concordant with CIn. 1‐h (CCr + CUN)/2 can estimate GFR accurately and precisely, making it a simple and speedy test for use in clinical practice. SUMMARY AT A GLANCE: The importance of better measures of kidney function in children is highlighted in this cross‐sectional study, which evaluated the use of a 1‐h urine collection for the determination of the mean of creatinine clearance and urea clearance, and showed a good agreement with measured inulin clearance. The authors propose this urine collection as a quick and reliable measure of kidney function in children and suggest that it may be more accurate than other endogenous clearance methods. [ABSTRACT FROM AUTHOR]