Imaging Indications for Pediatric UTI
Imaging recommendations for pediatric UTI are highly age-dependent, with renal and bladder ultrasound being the primary initial study for most children, while routine imaging is generally not indicated for children >6 years with uncomplicated first febrile UTI. 1
Age-Based Imaging Algorithm
Infants <2 Months of Age
Renal and bladder ultrasound (RBUS) is the essential first-line imaging study for all infants <2 months with first febrile UTI 1. This age group has the highest risk for underlying urologic abnormalities and bacteremia (4-36.4% of cases) 2.
For male infants specifically:
- Voiding cystourethrography (VCUG) should be strongly considered to exclude posterior urethral valves and detect vesicoureteral reflux (VUR), which is more common in males 1
- VCUG can be safely avoided if the infant has E. coli infection, normal RBUS, and is <3 months old 1
- If RBUS is abnormal, poor urine flow exists, or family history of VUR is present, VCUG becomes more important 1
For female infants:
- Nuclear medicine cystography may be considered as an alternative to VCUG (lower radiation exposure) 1
DMSA renal scan considerations:
- Can be performed acutely to detect pyelonephritis; if normal, VCUG may be avoided in >50% of cases 1
- However, NICE guidelines do not recommend DMSA for infants <6 months responding well to treatment within 48 hours 1
Children 2 Months to 6 Years
RBUS is the primary imaging study recommended after first febrile UTI 1. The American Academy of Pediatrics specifically recommends RBUS for children 2-24 months with febrile UTI 1.
Important caveat: RBUS has poor sensitivity (5-28%) for detecting VUR and should not be considered a screening test for genitourinary abnormalities 3. RBUS and VCUG provide complementary but different information 3.
VCUG indications in this age group:
- After second febrile UTI (AAP guidelines) 1
- After first febrile UTI if RBUS shows abnormalities 1
- For children <6 months with atypical UTI 1
- For children 6 months to 3 years with atypical UTI AND abnormal RBUS, poor urine flow, or family history of VUR 1
Timing considerations for RBUS:
- Delaying RBUS reduces false-positive dilation findings; for each additional day of delay, odds of detecting dilation decrease by approximately 2% 4
- This suggests waiting until acute inflammation resolves may prevent unnecessary follow-up testing 4
Children >6 Years of Age
No routine imaging is indicated for first febrile UTI with appropriate response to treatment 1. The incidence of new-onset UTI is low in this age group and typically associated with behavioral abnormalities, dysfunctional elimination syndrome, or sexual activity in adolescents 1.
Exceptions requiring RBUS:
- Poor urine flow 1
- Abdominal or bladder mass 1
- Elevated creatinine 1
- Septicemia 1
- Failure to respond to appropriate antibiotics within 48 hours 1
- Non-E. coli organisms 1
Consensus opinion: Despite lack of evidence, RBUS may still be useful based on common clinical practice 1
Atypical or Recurrent UTI (Any Age)
Atypical UTI is defined as: seriously ill appearance, poor urine flow, abdominal/bladder mass, elevated creatinine, septicemia, failure to respond within 48 hours, or non-E. coli infection 2.
Recurrent UTI is defined as: ≥2 episodes of pyelonephritis, OR 1 pyelonephritis plus ≥1 cystitis episode, OR ≥3 cystitis episodes 2.
Recommended imaging:
- RBUS is usually appropriate to detect underlying abnormalities, calculi, or complications like renal/perirenal abscess 1
- VCUG or voiding urosonography (VUS) is usually appropriate given increased VUR prevalence (35-74% in recurrent UTI) 1
- Nuclear medicine cystography may be appropriate (though evidence is older than other modalities) 1
CT abdomen/pelvis with IV contrast:
- Reserved for suspected complications such as renal abscess or xanthogranulomatous pyelonephritis 1
- Not for routine evaluation 1
DMSA renal scan:
- Recommended 4-6 months after atypical/recurrent infection in children <3 years 1
- For recurrent infection in children >3 years 1
- Normal DMSA may exclude high-grade reflux and avoid invasive VCUG 1
- Approximately 15% of children develop renal scarring after first UTI 2
Follow-Up Imaging for Established VUR
Multiple modalities are appropriate:
- RBUS every 12 months to monitor renal growth and parenchymal scarring (detects ~40% of scarring) 1
- VUS, VCUG, or nuclear medicine cystography for reflux reassessment 1
- Longer intervals between studies for lower-grade VUR; shorter for grades III-V, bladder/bowel dysfunction, or older age 1
DMSA considerations:
- May be appropriate to detect new renal scarring, especially after febrile UTI or when RBUS is abnormal 1
Key Pitfalls to Avoid
- Do not use RBUS as a screening test for VUR—it has very poor sensitivity and provides different information than VCUG 3
- Do not perform RBUS too early—acute inflammation causes false-positive dilation findings 4
- Do not routinely image children >6 years with uncomplicated first UTI—yield is extremely low 1
- Do not skip VCUG in male infants <2 months—posterior urethral valves must be excluded 1
- Do not order CT routinely—reserve for suspected complications only 1