What diagnostic testing is recommended for a patient with intermittent non-radiating flank pain, urinary frequency, and tenderness on palpation, with negative pregnancy test and urinalysis, and no fever?

Diagnostic Testing for Intermittent Non-Radiating Flank Pain with Negative Urinalysis

Non-contrast CT of the abdomen and pelvis is the recommended initial diagnostic test for a patient with intermittent non-radiating flank pain, urinary frequency, and tenderness on palpation, despite negative pregnancy test, urinalysis, and absence of fever. 1, 2

Rationale for Non-contrast CT

• Gold standard for urolithiasis detection with sensitivity up to 97% 2
• Can identify alternative diagnoses in approximately one-third of patients with acute flank pain 3
• Provides detailed information about:
  • Stone size and location (critical for management decisions)
  • Secondary signs of obstruction
  • Periureteral and perinephric inflammation
  • Alternative diagnoses that may mimic urolithiasis symptoms

Alternative Imaging Options

If radiation exposure is a concern or CT is unavailable:

Ultrasound

• Reasonable alternative with sensitivity up to 100% and specificity up to 90% for diagnosing ureteral obstruction 2
• Improved sensitivity for small renal stones (up to 99% for stones <5mm) when combined with color Doppler and twinkling artifact assessment 1, 2
• Less sensitive than CT for direct stone visualization, with overall sensitivity of 24-57% for stone detection 1

Combined Ultrasound and Radiography

• Combination yields sensitivity of approximately 79% for detecting clinically significant stones 1
• Provides an acceptable alternative to CT for some patients 1

Important Clinical Considerations

Negative Urinalysis Interpretation

• Despite the negative urinalysis in this case, urolithiasis remains a possibility
• Up to 10-15% of patients with confirmed urolithiasis may have a negative urinalysis
• The absence of hematuria does not exclude stone disease, especially with:
  • Intermittent obstruction
  • Complete obstruction
  • Dehydration

Alternative Diagnoses to Consider

• Right colonic diverticulitis (accounts for 8% of right lower quadrant pain cases) 2
• Bowel obstruction (3% of right lower quadrant pain cases) 2
• Musculoskeletal causes of flank pain
• Gynecological conditions (despite negative pregnancy test)
• Renal infarction or other vascular pathologies

Diagnostic Algorithm

1. First-line imaging: Non-contrast CT abdomen and pelvis
2. If CT contraindicated or unavailable: Ultrasound of kidneys, ureters, and bladder with color Doppler
3. If ultrasound is negative but symptoms persist: Consider contrast-enhanced CT or MR urography

Common Pitfalls to Avoid

• Relying solely on urinalysis to rule out urolithiasis
• Assuming that absence of fever excludes infection (early or partially treated infections may be afebrile)
• Overlooking non-urological causes of flank pain
• Failing to consider contrast-enhanced imaging when non-contrast studies are inconclusive

The American College of Radiology consistently recommends non-contrast CT as the initial imaging modality for acute flank pain with suspected stone disease, even in cases with atypical presentations or negative urinalysis 1.