Objective To assess the effect of the duration of fever after the initiation of treatment (FAT) of febrile urinary tract infections (UTI) on the development of permanent renal lesions based on dimercaptosuccinic acid (DMSA) scintigraphy findings. To evaluate the FAT contribution to permanent renal lesion formation in relation to fever before treatment initiation (FBT), the presence of vesicourinary reflux (VUR), age and severity of infection.

Methods The inpatient records of 148 children (median age: 2.4 months (11 days to 24 months)) with a first episode of UTI during a 3-year period were analysed. DMSA findings, and clinical and laboratory parameters were evaluated.

Results Among the study population, 34/148 (22.97%) children had permanent renal lesions on the DMSA scan 6 months after a single episode of UTI. Twenty-three children (15.5%) had mild, 10 (6.7%) had moderate and 1 (0.6%) child had severe lesions on the DMSA. FAT prolongation >/48 hours was associated with older age (p=0.01) and increased absolute neutrophil count (p=0.042). The likelihood of lesions was significantly increased when FAT was ≥48 hours (R²=0.043, p=0.021). On multiple regression analysis, with the addition of FBT>/72 hours (0.022), the presence of VUR (p<0.001), C-reactive protein (p=0.027) and age (p=0.031), the effect of FAT on lesion development disappeared (p=0.15).

Conclusions Prolongation of FAT≥48 hours of febrile UTI in children <2 years significantly contributes to the development of permanent renal lesions. However, delay in treatment initiation >/72 hours, the presence of VUR, older age and infection severity seem to be more significant predictors of the development of renal lesions.