Imaging Recommendations for Recurrent Urinary Tract Infections
For patients with recurrent urinary tract infections (UTIs), no routine imaging is recommended for uncomplicated cases, while CT urography (CTU) or MR urography (MRU) are the preferred imaging modalities for complicated cases. 1, 2
Imaging Algorithm Based on UTI Classification
Uncomplicated Recurrent UTIs
- No imaging is typically necessary for patients with uncomplicated recurrent UTIs and no risk factors 1
- Most women with uncomplicated recurrent UTIs have normal urinary tracts and do not benefit from routine imaging 1
Complicated Recurrent UTIs
Imaging is indicated for patients with:
- Non-response to conventional therapy
- Frequent reinfections or relapses
- Known underlying risk factors (e.g., urinary tract abnormalities, immunocompromise)
- Age >50 years with risk factors for urinary tract malignancy 1
First-Line Imaging for Complicated UTIs
CT Urography (CTU)
- Primary recommended test for complicated recurrent UTIs 1
- Includes:
- Unenhanced phase
- Nephrographic phase
- Excretory phase with detailed anatomic depiction of kidneys, collecting systems, ureters, and bladder
- Diuretic administration prior to excretory phase improves urinary tract distention and opacification 1
- Excellent sensitivity and specificity for:
- Renal and urothelial lesions
- Congenital anomalies
- Urinary tract obstruction
- Calculi (100% sensitivity) 1
MR Urography (MRU)
- Equivalent alternative to CTU for complicated recurrent UTIs 1, 2
- Advantages:
- No radiation exposure
- More functional information than CT
- Superior for soft tissue contrast
- Better for diagnosing active infection versus scarring
- Excellent for urethral diverticula assessment and surgical planning 1
- Limitations:
Special Considerations
Age-Based Recommendations
- Patients <30 years without risk factors for malignancy: Ultrasound or non-contrast CT may be appropriate first-line examinations 1
- Patients >50 years with risk factors for urinary tract malignancy: CTU is preferred 1
Patients with Renal Impairment
- For patients at risk of contrast-induced nephropathy:
- Ultrasound can be considered as an alternative imaging modality 2
- If contrast is necessary, implement preventive measures:
- Adequate hydration with isotonic saline (0.9% NaCl) at 1 ml/kg/h for 12 hours before and 24 hours after procedure
- Use low-osmolar or iso-osmolar contrast media
- Minimize contrast volume (<350 mL or <4 mL/kg)
- Temporarily suspend nephrotoxic medications 2
Role of Other Imaging Modalities
Ultrasound
- Useful initial screening tool for:
- Hydronephrosis and obstructive uropathy
- Post-void residual volume determination
- Renal abscess or perinephric collections
- Bladder diverticula 1
- Limited sensitivity for detecting specific etiologies of obstruction and smaller calculi 1, 3
- Low diagnostic accuracy as standalone test (43.33% total accuracy) 3
Voiding Cystourethrography
- Consider when:
- Bladder diverticulum is at/near ureteral orifice (to evaluate vesicoureteral reflux)
- Suspected bladder/urethral fistula
- Urethral diverticulum
- Bladder prolapse 1
Intravenous Urography (IVU)
- Largely replaced by CT and MRI at most institutions 1, 2
- Not recommended for evaluation of recurrent UTIs 1
Common Pitfalls to Avoid
Overimaging uncomplicated cases: Most women with uncomplicated recurrent UTIs have normal urinary tracts and do not require imaging 1, 4
Using outdated imaging modalities: IVU has been largely replaced by CT and MRI 1, 2
Relying solely on ultrasound: While useful as a screening tool, ultrasound alone has limited sensitivity and specificity (sensitivity 66.7%, specificity 37.5%) for comprehensive evaluation 3
Ignoring renal function: For patients with impaired renal function, appropriate contrast precautions or alternative imaging should be considered 2