Evaluation of renal function in children with solid tumors: Comparison between estimation with Schwartz formula and EDTA clearance.

Abstract

9560 Background: Using the [51Cr]-ethylenediamine tetra acetic acid ([51Cr]-EDTA) method provides an accurate measure of glomerular filtration rate (GFR) for each patient. However, this method is not always feasible in routine. Thus, several mathematical equations have been developed to predict creatinine clearance. The most widely used in pediatric patients is the Schwartz formula, based on patient height and serum creatinine. However, this method has not been validated in pediatric cancer patients. The aim of the present study was to compare GFR measured with the 51Cr-EDTA method to GFR estimated with the Schwartz formula in patients younger than 18 years of age and treated for solid tumors. Methods: Data have been retrospectively collected on consecutive children treated between 2001 and 2011 at Institut Gustave Roussy. All of the patients had undergone assessment of GFR via 51Cr-EDTA clearance and estimation of renal function by the Schwartz formula. Exclusion criteria were serum creatinine under 25µmol/L or no recent dosage available. GFR analysis was realized using the slope intercept method after a single injection of 51Cr-EDTA solution.. Values of the GFR were calculated by multiplying the volume of dilution by the slope of the single exponential fit to the three data points and then expressed in ml/min/1.73m². Student paired t-test (alpha = 0.05) was used to compare results obtained for each patient with the two methods. Results: 196 patients (120 males, 76 females), treated with various types of cancer (neuroblastoma, osteosarcoma, Ewing sarcoma, lymphoma…) Mean age was 6.7 years. Mean GFR was 127.5 ml/min/1.73m² with the 51Cr-EDTA method versus 148.1 ml/min/1.73m² with the Schwartz formula. Mean of difference was 20.7 ml/min/1.73m² with a confidence interval [-25.7 ; -15.6] (p < 0.0001). Conclusions: GFR estimated with the Schwartz formula is statistically different from the isotopic method. In most cases, GFR estimated with the Schwartz formula is overestimated. This study highlights the lack of accuracy of this equation in pediatric population with cancer. The 51Cr-EDTA method must be preferred when a reliable and accurate evaluation of renal function is needed.