Timing of Renal and Bladder Ultrasound After First Febrile Urinary Tract Infection: A Hospitalist Dilemma

Renal/bladder ultrasonography (RBUS) is often obtained before discharge in hospitalized children with first febrile urinary tract infection (fUTI). However, dilatation or uroepithelial thickening (UET) during infection may be transient and thus confound interpretation. We aimed to examine practice patterns of timing of RBUS, assess the significance of abnormal findings relative to fever, and identify the incidence of patient lost to follow-up.

We performed a multicenter, retrospective study of previously healthy children aged 2 to 24 months hospitalized for first fUTI in 2018 through 2022. We compared ultrasonography results obtained less than 24 hours ("early") vs 24 hours or more ("late") from last fever and evaluated the impact of timing on frequency of abnormalities in ultrasonography findings. Children were considered lost to follow-up if RBUS was not performed within 6 months.

Two hundred ninety-four children were included. Two-hundred eighty-two (95.9%) had an ultrasonography (267 [90.8%] during hospitalization); 177 (62.8%) were performed early, 81 (28.7%) late. Abnormalities were more frequent among early (64.4%) than late (40.7%) findings. Specifically, UET was more frequent among early (18.6%) than late (4.9%) ultrasonography findings (P = .004). Ultrasonography results prompted a voiding cystourethrogram (VCUG) in 72 children. In the early ultrasonography group, 29 of 53 (54.7%) VCUG findings were normal, compared with 6 of 13 (46.2%) in the late group (P = .579). Twelve of 27 (44.4%) children were lost to follow-up when RBUS was not performed inpatient.

RBUS obtained while the patient was febrile or shortly thereafter was more likely to reveal dilatation and UET, which may be related to transient inflammation from the acute infection. Further prospective studies are needed to confirm these findings and to determine optimal RBUS timing, given the limitations of a retrospective design.