Should a plain kidney‑ureter‑bladder X‑ray be obtained for an 11‑month‑old infant presenting with a urinary tract infection?

KUB Is Not Indicated for UTI in an 11-Month-Old

A plain kidney-ureter-bladder (KUB) X-ray has no role in the evaluation of urinary tract infection in an 11-month-old infant and should not be obtained. 1

Recommended Imaging for This Age Group

Renal and Bladder Ultrasound – The Only Appropriate Initial Study

• Renal and bladder ultrasound is the first-line and primary imaging modality for infants under 2 years with a first febrile UTI, rated 9/9 ("usually appropriate") by the American College of Radiology. 1

• Ultrasound detects anatomic abnormalities such as hydronephrosis (found in 45% of neonates with UTI), obstruction, renal duplication, and structural anomalies that influence management. 1

• This study involves no ionizing radiation, making it the safest option for infants. 1

• The ultrasound should be obtained within 6 weeks of the UTI if the infection is typical, or during the acute infection if atypical (poor response to antibiotics within 48 hours, septic appearance, non-E. coli organism, elevated creatinine, or poor urine flow). 1

Why KUB Is Not Mentioned in Any Guideline

• The 2024 ACR Appropriateness Criteria for pediatric UTI do not list KUB as an imaging option at any appropriateness level for children of any age with UTI. 1

• KUB provides no information about renal parenchyma, hydronephrosis, or vesicoureteral reflux—the key findings that alter management in pediatric UTI. 1

• Plain radiography cannot detect pyelonephritis, scarring, or functional abnormalities that ultrasound and other modalities can identify. 1

Additional Imaging Considerations

Voiding Cystourethrography (VCUG) – Selective Use Only

• VCUG is not routinely recommended after a first febrile UTI in an 11-month-old who responds well to treatment within 48 hours. 1

• VCUG should be performed only if:

  • The renal ultrasound shows hydronephrosis, scarring, or findings suggesting high-grade VUR or obstruction 1
  • There is a second febrile UTI 1
  • Fever persists beyond 48 hours of appropriate antibiotic therapy 1
  • The child is a male infant <2 months (to exclude posterior urethral valves) 1

• Recent data show that in children <3 months with first febrile UTI, E. coli in urine, and normal renal/bladder ultrasound, VCUG can be safely avoided. 1

DMSA Renal Scan – Not for Immediate Post-Treatment

• DMSA scan should be deferred until 4-6 months after infection to evaluate for renal scarring, not performed acutely. 1

• The ACR rates DMSA as 3/9 ("usually not appropriate") for immediate evaluation after a first febrile UTI with good response. 1

Clinical Context

Why Imaging Matters in This Age Group

• Infants <2 years have an increased incidence of sepsis and renal anomalies associated with UTIs compared to older children. 1

• Approximately 15% of children develop renal scarring after a first UTI, which can lead to hypertension (5%) and chronic kidney disease (3.5% of ESRD cases). 2

• Early antibiotic treatment within 48 hours of fever onset reduces renal scarring risk by more than 50%. 2, 3

Common Pitfalls to Avoid

• Do not order a KUB for pediatric UTI—it provides no clinically useful information and exposes the child to unnecessary radiation. 1

• Do not skip the renal ultrasound in an 11-month-old with febrile UTI, as this is the only way to detect anatomic abnormalities that require further evaluation. 1

• Do not routinely order VCUG after a first UTI unless specific indications are present (abnormal ultrasound, recurrent infection, or poor clinical response). 1

• Do not order CT for routine UTI evaluation—reserve it only for suspected complications such as renal abscess. 1