From the Guidelines
Renal and urinary tract ultrasound is recommended for all infants and young children (under 2-3 years) after their first febrile UTI, and for older children with recurrent UTIs, atypical presentations, or poor response to treatment. The most recent and highest quality study, 1, published in 2024, supports the use of ultrasound in children under 6 months of age within 6 weeks of the UTI if typical infection or during the acute infection if an atypical infection.
Indications for Ultrasound
The indications for renal and urinary tract ultrasound in pediatric patients with UTIs include:
- Infants and young children (under 2-3 years) after their first febrile UTI
- Older children with recurrent UTIs, atypical presentations, or poor response to treatment
- Infants with febrile UTIs who appear severely ill, have poor urine flow, abdominal or bladder masses, elevated creatinine, sepsis, or fail to respond to appropriate antibiotic therapy within 48-72 hours
Timing of Ultrasound
The ultrasound should be performed within 2-6 weeks after the acute infection has resolved to avoid false findings from acute inflammation, as suggested by 1 and 1.
Benefits of Ultrasound
Ultrasound is preferred as the initial imaging study because it avoids radiation exposure while providing valuable anatomical information to guide further management decisions, as noted in 1. It helps identify structural abnormalities such as hydronephrosis, renal scarring, duplicated collecting systems, ureteroceles, posterior urethral valves, and vesicoureteral reflux that may predispose children to recurrent infections.
Limitations of Ultrasound
The main limitations of ultrasound are the detection of pyelonephritis, scarring, and VUR, with a low sensitivity (76.5%) for detecting VUR and renal scarring, as reported in 1. However, the sensitivity of ultrasound for the detection of findings suggestive of high-grade VUR is markedly improved when uroepithelial thickening is considered.
Clinical Decision-Making
The rationale for ultrasound imaging is to detect conditions requiring surgical intervention or additional management beyond antibiotics, as approximately 30% of children with first-time UTIs have underlying urological abnormalities, as mentioned in 1. Ultrasound imaging should be used to guide further management decisions, taking into account the potential benefits and limitations of the imaging modality.
From the Research
Indications for Renal and Urinary Tract Ultrasound in Pediatric Patients with UTIs
The following are indications for renal and urinary tract ultrasound in pediatric patients with urinary tract infections (UTIs):
- Febrile UTI in infants aged 2-24 months 2, 3
- First episode of UTI in children aged 2-24 months 2, 3
- Presence of urinary tract dilatation or other abnormalities on initial ultrasound 4
- Suspicion of vesicoureteral reflux (VUR) or obstructive lesions 4
- Abnormal findings on voiding cystourethrography (VCUG) 2, 4
Ultrasound Findings and Management
Ultrasound findings can influence management in some cases, including:
- Detection of significant non-reflux abnormalities in the kidneys and urinary tract 5
- Identification of patients who may require operative treatment 5
- Guidance for antimicrobial prophylaxis and other urological treatment 2
Timing and Yield of Ultrasound
The timing of ultrasound relative to the acute illness can affect the yield of abnormal findings:
- Delaying ultrasound may lead to fewer false-positive results and reduced healthcare costs 3
- The yield of ultrasound in detecting renal abnormalities and VUR can be measured by its sensitivity, specificity, and predictive values 6
Clinical Practice and Guidelines
The American Academy of Pediatrics (AAP) guidelines recommend renal and bladder ultrasonography (RBUS) after the first febrile UTI in infants aged 2-24 months 2, 3
- The AAP guidelines seem applicable to clinical practice, with indications for RBUS and VCUG based on patient age, symptoms, and ultrasound findings 2