Risk factors for renal scar formation in infants with first episode of acute pyelonephritis: a prospective clinical study.

PURPOSE: We prospectively determined the risk factors for renal scar formation after the first episode of acute pyelonephritis as confirmed on dimercapto-succinic acid scintigraphy in children younger than 1 year.

MATERIALS AND METHODS: A total of 213 infants with acute pyelonephritis were enrolled in the study. Infants with urological abnormalities other than vesicoureteral reflux were excluded from analysis. Followup scanning was performed 6 months after acute pyelonephritis and voiding cystourethrography was performed after the acute phase of infection. Possible risk factors were evaluated including gender, peak fever, duration of fever before and after treatment with antibiotics, white blood cell count, C-reactive protein concentration, presence of vesicoureteral reflux and reflux grade.

RESULTS: Six months after acute pyelonephritis 37 of 213 (17.4%) infants and 41 of 248 (16.5%) renal units with acute photon defects on initial dimercapto-succinic acid scintigraphy had renal scars. The rates of scar formation were significantly higher in infants with vesicoureteral reflux than in those without (39.4% vs 7.5%, p <0.001, OR 9.433) and in renal units with vesicoureteral reflux than in those without (39.4% vs 8.2%, p <0.001, OR 7.237). Renal scar formation was related to reflux grade (none-8.2%, grade I-20%, grade II-22.7%, grade III-40%, grade IV-70%, grade V-55.6%, p <0.001) but not to any other clinical or laboratory variables.

CONCLUSIONS: The presence of vesicoureteral reflux was the only independent risk factor for renal scar formation after acute pyelonephritis in infants. The prevalence of renal scarring was significantly correlated with reflux grade. Voiding cystourethrography is necessary in infants after the first acute pyelonephritis episode is confirmed on dimercapto-succinic acid renal scintigraphy.