Would you treat a patient with intermittent flank pain, urinary frequency, hematuria, and leukocyte esterase in urine as a Urinary Tract Infection (UTI) or work up for a kidney stone?

Management of Intermittent Flank Pain with Urinary Symptoms: UTI vs. Kidney Stone

For a patient with intermittent flank pain, urinary frequency, hematuria, and leukocyte esterase in urine, you should work up for kidney stone first while simultaneously initiating empiric UTI treatment. This approach addresses both potential diagnoses, as these symptoms strongly suggest either pyelonephritis or nephrolithiasis, which can coexist.

Diagnostic Approach

Initial Assessment

• Symptom pattern: Intermittent flank pain suggests possible kidney stone, while frequency and hematuria could indicate either UTI or stone
• Leukocyte esterase: Indicates inflammation but has low positive predictive value for infection alone 1
• Hematuria: Present in both conditions but more characteristic of stones

Recommended Diagnostic Tests

1. Non-contrast CT scan: Gold standard for kidney stone diagnosis

   • Highest sensitivity and specificity for urolithiasis 2
   • Can identify stone size, location, and potential obstruction
   • Can also detect other causes of flank pain 3

2. Urine culture: To confirm infection and guide targeted therapy

   • Essential for suspected pyelonephritis 1
   • Identifies specific pathogens and antimicrobial susceptibility

Treatment Algorithm

Step 1: Empiric Treatment

• Start empiric antibiotic therapy while awaiting imaging and culture results
• Recommended regimens for suspected pyelonephritis 1:
  • Oral therapy (if stable): Fluoroquinolone (if local resistance <10%) or trimethoprim-sulfamethoxazole (if susceptible)
  • IV therapy (if systemic symptoms): Amoxicillin plus aminoglycoside or third-generation cephalosporin

Step 2: Based on Imaging Results

• If stone identified:

  • Size <10mm: Consider medical expulsive therapy with alpha blockers 4
  • Size >10mm or obstructing: Urological consultation for possible intervention
  • If concurrent infection with obstruction: Urgent drainage required 4

• If no stone but signs of pyelonephritis:

  • Complete antibiotic course (7-14 days) 1
  • Consider urological evaluation if recurrent episodes

Step 3: Follow-up

• Reassess symptoms after 48-72 hours
• Adjust antibiotics based on culture results
• Consider metabolic evaluation if kidney stone confirmed

Important Considerations

When to Suspect Both Conditions

• Kidney stones can cause secondary infection due to urinary stasis and obstruction 5
• Infection stones (struvite) can form due to urease-producing bacteria 5
• The combination of stone and infection significantly increases morbidity risk

Red Flags Requiring Urgent Intervention

• Fever >38°C with flank pain
• Signs of sepsis or systemic inflammatory response
• Evidence of obstructive uropathy
• Single functioning kidney
• Immunocompromised status

Pitfalls to Avoid

1. Don't assume UTI without imaging: Relying solely on urinalysis can miss stones and other serious conditions 3

2. Don't delay imaging in severe cases: Obstruction with infection is a urological emergency requiring prompt decompression 4

3. Don't miss atypical presentations: Intermittent flank pain can also indicate ureteropelvic junction obstruction or other rare conditions 6

4. Don't treat asymptomatic bacteriuria: Positive urine cultures without symptoms should not be treated except in specific circumstances 1

By following this approach, you address both potential diagnoses while prioritizing the condition most likely to cause significant morbidity if left untreated.