The clinical decision rule proposed in its current form that, for children aged 1 month to 4 years with a first febrile UTI, cystography should be performed in cases with ureteral dilation (i.e., ureter visible whatever its dilation) and a serum PCT level ≥0.17 ng/mL, or without ureteral dilatation (i.e., ureter not visible) when the serum PCT level ≥0.63 ng/mL. The gene discussed is CALCA; the disease is bacterial urinary tract infection.