In a child with recurrent urinary tract infections presenting with dysuria and a urinalysis positive for nitrites and leukocytes, which imaging study is the most appropriate initial investigation?

Imaging for Pediatric Recurrent UTI

In a child with recurrent urinary tract infections, both renal ultrasound AND voiding cystourethrogram are usually appropriate initial investigations—the answer is C.

Evidence-Based Rationale

The 2024 American College of Radiology Appropriateness Criteria explicitly address this exact clinical scenario under "Variant 5: atypical or recurrent febrile UTI in a child." 1 For recurrent UTI, both US of kidneys and bladder AND fluoroscopic VCUG are rated as "usually appropriate" for initial imaging. 1 This dual approach reflects the complementary nature of these studies: ultrasound detects anatomic abnormalities, obstruction, and scarring, while VCUG identifies vesicoureteral reflux (VUR)—a critical finding in recurrent UTI. 1

Why Both Studies Are Necessary

Renal Ultrasound Detects:

• Anatomic abnormalities (hydronephrosis, renal duplication, obstruction) that predispose to recurrent infection 1
• Renal scarring from previous infections (though sensitivity is only ~40%) 1
• Complications such as renal or perirenal abscess 1

VCUG Identifies:

• Vesicoureteral reflux, which has significantly higher prevalence in recurrent UTI 1
• The prevalence of grade IV-V VUR increases to approximately 18% after a second UTI 2
• Bladder and urethral abnormalities that may contribute to recurrent infection 1

Critical Evidence: These Studies Are Complementary, Not Redundant

Research demonstrates that ultrasound is a poor screening test for VUR. 3, 4 In a large study of 2,259 children with UTI, RBUS had sensitivity of only 5-28% for detecting any VUR and 18-55% for high-grade VUR (grade >III). 3 Even sophisticated predictive models using multiple ultrasound findings achieved poor accuracy (AUROC 0.57-0.79). 4 This means a normal ultrasound does NOT exclude VUR—you need VCUG to detect reflux. 3, 4

Conversely, VCUG does not visualize renal parenchyma, scarring, or many anatomic abnormalities that ultrasound readily identifies. 1 The 2024 ACR guidelines explicitly state: "RBUS and VCUG should be considered complementary as they provide important, but different, information." 1

Why Not Ultrasound Alone (Answer B)?

While ultrasound is appropriate, ordering only ultrasound would miss VUR in the majority of cases. 3, 4 Given that this child has recurrent UTI (not a first episode), the pre-test probability of VUR is substantially elevated, making VCUG essential. 1, 2 The ACR specifically rates VCUG as "usually appropriate" (not optional) for recurrent UTI. 1

Why Not VCUG Alone (Answer A)?

VCUG alone would miss:

• Renal scarring from previous infections 1
• Obstructive uropathy (e.g., ureteropelvic junction obstruction) 1
• Renal calculi or other anatomic abnormalities 1
• Complications such as abscess formation 1

Clinical Context: Recurrent vs. First UTI

The approach differs dramatically based on UTI history:

First UTI (not this case):

• Children >6 years: No routine imaging recommended 1
• Children 2-24 months: Ultrasound usually appropriate; VCUG only if ultrasound abnormal or after second UTI 1, 2

Recurrent UTI (this case):

• Both ultrasound AND VCUG are usually appropriate regardless of age 1
• This reflects the higher risk of underlying anatomic abnormalities and VUR 1

Practical Implementation

Order both studies together at the time of diagnosis of recurrent UTI. 1 Do not wait for ultrasound results before ordering VCUG, as this delays diagnosis and may require a second visit. 1 The studies can be performed on different days but should both be completed as part of the initial evaluation. 1

Timing Considerations:

• Ultrasound can be performed immediately or after acute infection resolves 5
• VCUG should be performed after the acute infection has been treated and the child is clinically well 1

Common Pitfalls to Avoid

• Do not assume a normal ultrasound excludes VUR—sensitivity is only 5-28% 3, 4
• Do not delay VCUG waiting to see if UTIs recur again—by definition, this child already has recurrent UTI 1
• Do not order only KUB ultrasound (answer D)—this is not a standard imaging modality for UTI evaluation and would miss both VUR and detailed renal assessment 1

Long-Term Implications

Approximately 15% of children develop renal scarring after first UTI, which can lead to hypertension (5%) and chronic kidney disease (3.5% of ESRD cases). 2 Early detection of VUR and anatomic abnormalities through comprehensive imaging allows for appropriate management (prophylactic antibiotics for high-grade VUR, surgical correction of obstruction) to prevent progressive renal damage. 1, 2