Validity of the use of Schwartz formula against creatinine clearance in the assessment of renal functions in children

Abstract

Introduction: Glomerular filtration rate (GFR) is used as a measure of overall renal function. Creatinine clearance (CrCl) based estimation of GFR requires a 24-hour collection of urine which is cumbersome and time consuming. Instead, Schwartz formula is used for the estimation of GFR based on calculations. It is an estimate of GFR (eGFR) in children, derived from body length (L, in cm), serum creatinine (Scr, in mg/dL) and a constant (k = 0.55): GFR = (0.55 × L) /Scr. However, it is important to cross validate this equation before using it in Sri Lankan children. Objective: To cross validate the use of Schwartz formula against CrCl, in a paediatric population in determining the glomerular function. Method: A cross-sectional descriptive study was carried out at Lady Ridgeway Hospital for Children, Colombo, Sri Lanka. Forty seven children with chronic kidney disease from medical wards and nephrology clinic and 26 healthy children, between the ages of 3-12 years were recruited. In these patients GFR was determined using CrCl and calculated GFR by Schwartz formula using serum creatinine measure. The CrCl values were compared against eGFR derived from Schwartz formula. Correlation and limits of agreement between the two methods were evaluated. Results: Although a weak but statistically significant correlation (r = 0.476, P<0.001) was observed between GFR determined by CrCl and that estimated by Schwartz formula in the whole population, Bland Altman plot showed that the two tests had acceptable limits of agreement in lower GFR values but the limits became wider at higher GFR values. Conclusions: A weak but statistically significant correlation was seen between eGFR based on CrCl and eGFR derived from Schwartz formula.