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 (C Cr ) and urea clearance (C UN ) examined over a 1‐h urine collection period (1‐h (C Cr  + C UN )/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 (C In ) 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 (C Cr  + C UN )/2, 1‐h C Cr , 1‐h C UN and GFR estimated by Cr‐based and cystatin C (CysC)‐based formulas for Japanese children were compared with C In . Bland–Altman plots were used to evaluate correlations. The primary outcome measure was the correlation between 1‐h (C Cr  + C UN )/2 and C In . Results Fifty‐three children were analysed. Their median age was 10.9 (interquartile range [IQR] 5.3–14.2) years, and median C In and 1‐h (C Cr  + C UN )/2 were 77.0 (IQR: 51.5–95.1) and 81.0 (IQR: 64.1–97.7) ml/min/1.73 m 2 , respectively. Percentage difference of C In and 1‐h (C Cr  + C UN )/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 (C Cr  + C UN )/2 was 1.12 times C In . Conclusion 1 h (C Cr  + C UN )/2 was almost concordant with C In . 1‐h (C Cr  + C UN )/2 can estimate GFR accurately and precisely, making it a simple and speedy test for use in clinical practice.