Basal renal function in paediatric patients: correlation of methods that depend on a 24 h urine collection with simpler methods that do not require a timed urine

Introduction: In daily clinical practice a quick, easy and accessible method is needed to adequately assess renal function. The objectives of this study were: 1. To quantify the relationship and concordance of the glomerular filtration rate (GF) calculated by the clearance of creatinine in 24 h urine (CCr) and the original and modified Schwartz equation (SE); and 2. To correlate urine elimination of substances that depends on the volume of excreted urine in a unit of time with other parameters that are calculated measuring the concentration of these substances in blood and urine. Material and methods: The study included 401 healthy children with ages between 3 to 14 years (187 male and 214 female). The analysis between the variables was carried out using Pearson's correlation coefficient and the intraclass correlation coefficient (ICC). Results: The correlation between values of CCr and the original SE (non-standardised creatinine measurement) was r = 0.58 (P < 0.001) and the concordance, ICC = 0.74. The correlation between CCr values and the modified SE (standardised creatinine measurement) was r =0.68 (P<.001), and the concordance ICC = 0.78. There was a very significant correlation between the elimination of sodium in a 24h urine (mEq/kg/24 h) and the Na-Fractional-Excretion (EFNa): r =0.8 (P<.001). There was a correlation between the potassium elimination in 24 h (mEq/kg/24 h) and EFK: r = 0.85 (P<.001). Between volume/min/1.73 m(2) and the urine volume percent of GF was: r = 0.88 (P <.001). Conclusions: These equations provide valuable information of the state of the basal renal function without having to use a timed urine. (C) 2020 Asociacion Espanola de Pediatria. Published by Elsevier Espana, S.L.U.