Predictors of Abnormal Renal Ultrasonography in Children With Urinary Tract Infection.

Background and objectives: The 2011 American Academy of Pediatrics guidelines recommended a renal and bladder ultrasound (RBUS) after the first febrile urinary tract infection (UTI) in infants. Abnormal RBUS findings may be due to inflammation from the acute UTI or from vesicoureteral reflux (VUR), which may require a voiding cystourethrogram (VCUG) to diagnose, increasing health care costs. Our objective was to evaluate the effect of timing of imaging relative to the acute illness on abnormal dilation on RBUS and VCUG findings.

Methods: Multicenter, retrospective study of patients aged 2 to 24 months presenting with first UTI and RBUS from January 1, 2015, to December 31, 2019. Demographics, isolated pathogen, and timing of RBUS and VCUG relative to urine culture date were recorded and compared.

Results: A total of 227 patients were included. On multivariable logistic regression, increased time in days to RBUS was associated with decreased odds of abnormal dilation (adjusted odds ratio, 0.980; P = .018) in those patients meeting culture criteria for UTI (for each additional day of delay in obtaining RBUS, the adjusted odds of detecting dilation decreased by ∼2%). There was no significant association between timing of imaging and VUR on VCUG. Additionally, 32% of patients underwent RBUS who did not meet UTI culture criteria but had similar rates of abnormal dilation and VUR to those meeting UTI culture criteria.

Conclusions: Increased time to RBUS led to decreased odds of abnormal dilation, suggesting that delaying RBUS may lead to fewer false-positive results, which may limit unnecessary additional testing and reduce health care costs. Additionally, a significant number of patients who did not meet UTI culture criteria underwent RBUS but had similar results to those meeting criteria, suggesting that the previous colony-forming unit definition for UTI may be suboptimal.