Ultrasound as a screening test for genitourinary anomalies in children with UTI

Abstract

Background: The 2011 American Academy of Pediatrics guidelines state that renal and bladder ultrasound (RBUS) should be performed after initial febrile urinary tract infection (UTI) in a young child, with voiding cystourethrogram (VCUG) performed only if RBUS shows abnormalities. We sought to determine test characteristics and predictive values of RBUS for VCUG findings in this setting.

Methods: We analyzed 3995 clinical encounters from January 1, 2006 to December 31, 2010 during which VCUG and RBUS were performed for history of UTI. Patients who had previous postnatal genitourinary imaging or history of prenatal hydronephrosis were excluded. Sensitivity, specificity, and predictive values of RBUS for VCUG abnormalities were determined.

Results: We identified 2259 patients age <60 months who had UTI as the indication for imaging. RBUS was reported as "normal" in 75%. On VCUG, any vesicoureteral reflux (VUR) was identified in 41.7%, VUR grade >II in 20.9%, and VUR grade >III in 2.8%. Sensitivity of RBUS for any abnormal findings on VCUG ranged from 5% (specificity: 97%) to 28% (specificity: 77%). Sensitivity for VUR grade >III ranged from 18% (specificity: 97%) to 55% (specificity: 77%). Among the 1203 children aged 2 to 24 months imaged after a first febrile UTI, positive predictive value of RBUS was 37% to 47% for VUR grade >II (13% to 24% for VUR grade >III); negative predictive value was 72% to 74% for VUR grade >II (95% to 96% for VUR grade >III).

Conclusions: RBUS is a poor screening test for genitourinary abnormalities. RBUS and VCUG should be considered complementary as they provide important, but different, information.

Keywords: imaging; pediatrics; urinary tract infection; vesicoureteral reflux.

FIGURE 1

ROC curves for RBUS as a screening test for GU abnormalities on VCUG. Each graph represents specific VCUG outcome threshold. Points on each curve represent each RBUS thresholds A through D (see Table 1). A, ROC curve for VCUG-A (urethral findings or major bladder findings or VUR > grade III). Area under curve (AUC) = 0.674. B, ROC curve for VCUG-B (urethral findings or major bladder findings or VUR > grade II). AUC = 0.573. C, ROC curve for VCUG-C (urethral findings or major bladder findings or VUR > grade I). AUC = 0.532. D, ROC curve for VCUG-D (urethral findings or major bladder findings or any VUR). AUC = 0.527.