Comparison of the characteristics of the derivation and validation populations.

Values are expressed as n (%) for binary variables (gender, All grade and high-grade VUR, Ureteral dilation), and as: mean (±Standard deviation); median (inter-quartile range) for continuous variables (age, CPR, PCT).*Data in the column come from the previously published derivation of the decision rule [34].**Binary variables were compared using a χ2 test, and continuous variables were compared using the non-parametric Mann-Whitney test.Abbreviations: CRP, C-reactive protein; PCT, Procalcitonin; U dilation, Ureteral dilation; VUR, Vesico-ureteral reflux.