Renal Ultrasound for Infants Younger Than 2 Months With a Febrile Urinary Tract Infection

Abstract

Objective: The purpose of this study is to determine the performance of renal ultrasound for detecting vesicoureteral reflux (VUR) and obstructive uropathies in infants younger than 2 months with a febrile urinary tract infection (UTI).

Materials and methods: We performed a retrospective cohort study of infants younger than 2 months with fever and culture-proven UTI presenting from July 1, 2008, through December 31, 2011, with renal ultrasound and voiding cystourethrogram (VCUG) performed within 30 days of UTI diagnosis. Two pediatric radiologists independently reviewed the renal ultrasound and VCUG findings. Results of the renal ultrasound were deemed abnormal if collecting system dilation, renal size asymmetry, collecting system duplication, urothelial thickening, ureteral dilation, or bladder anomalies were present. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of renal ultrasound were calculated using VCUG as reference standard.

Results: Of the 197 patients included (mean [SD] age, 33 [ 15 ] days; male-to-female ratio, 2:1), 25% (n = 49) had VUR grades I-V, with 16% (n = 31) having VUR grades III-V and 8% (n = 15) having VUR grades IV-V. For grades I-V VUR, sensitivity was 32.7% (95% CI, 20.0-47.5%), specificity was 69.6% (95% CI, 61.5-76.9%), PPV was 26.2% (95% CI, 15.8-39.1%), and NPV was 75.7% (95% CI, 67.6-82.7%). For grades III-V VUR, sensitivity was 51.6% (95% CI, 33.1-69.9%), specificity was 72.9% (95% CI, 65.5-79.5%), PPV was 26.2% (95% CI, 15.8-39.1%), and NPV was 89.0% (95% CI, 82.5-93.7%). For grades IV-V VUR, sensitivity was 86.7% (95% CI, 59.5-98.3%), specificity was 73.6% (95% CI, 66.6-79.9%), PPV was 21.3% (95% CI, 11.9-33.7%), and NPV was 98.5% (95% CI, 94.8-99.8%). No obstructive uropathies were diagnosed by VCUG in patients with normal renal ultrasound findings.

Conclusion: In infants younger than 2 months, a normal renal ultrasound makes the presence of grades IV and V VUR highly unlikely but does not rule out lower grades of VUR.

Keywords: neonate; ultrasound; urinary tract infection; vesicoureteral reflux; voiding cystourethrogram.