What is the initial workup for a patient presenting with flank pain?

Initial Workup for Flank Pain

The initial workup for a patient presenting with flank pain should include a focused history, physical examination, urinalysis, and non-contrast CT scan of the abdomen and pelvis as the primary imaging modality due to its superior sensitivity and specificity for detecting urolithiasis and other causes of flank pain. 1

Clinical Assessment

History

• Timing and onset of pain (abrupt onset suggests renal colic)
• Location and radiation of pain (unilateral flank pain radiating to groin/genitals is typical for renal colic) 1
• Associated symptoms (nausea, vomiting, hematuria)
• Previous history of kidney stones or urinary tract disorders
• Risk factors for dangerous alternative diagnoses:
  • Age >60 years (consider abdominal aortic aneurysm)
  • Women with delayed menses (consider ectopic pregnancy) 1

Physical Examination

• Vital signs (fever suggests infection, hypotension suggests shock)
• Abdominal examination to determine site of maximal tenderness
• Assessment for peritoneal signs or other conditions mimicking flank pain
• Patients with shock or fever require immediate hospital admission 1

Laboratory Tests

• Urinalysis for hematuria (present in >80% of renal colic cases)
  • Positive hematuria supports diagnosis of urolithiasis
  • Negative hematuria should prompt consideration of alternative diagnoses 1
• Complete blood count (to assess for infection)
• Basic metabolic panel (to assess renal function)

Imaging Studies

First-Line Imaging

• Non-contrast CT of abdomen and pelvis
  • Sensitivity up to 97% for detecting urolithiasis 1
  • Can identify virtually all renal calculi regardless of composition
  • Can detect secondary signs of obstruction and complications
  • Can identify alternative diagnoses in patients without stones 2
  • Requires no contrast, minimizing risk of allergic reactions or nephrotoxicity 3

Alternative Imaging Options

• Ultrasound of kidneys and bladder

  • Consider in pregnant patients, children, or when radiation exposure is a concern
  • Less sensitive than CT (24-57% for stone detection) but 100% sensitive for diagnosing obstruction 1
  • Addition of color Doppler and twinkling artifact improves sensitivity for small stones 1
  • Can be combined with KUB radiography to improve stone detection 1

• CT with IV contrast

  • Not first-line for suspected urolithiasis as contrast may obscure stones
  • Consider when alternative diagnoses are strongly suspected 1
  • Useful when infection or other non-stone pathology is suspected 1

Management Decision Points

Criteria for Hospital Admission

• Failure to respond to analgesia within one hour
• Fever or signs of systemic infection
• Shock or hemodynamic instability
• Intractable vomiting or inability to maintain hydration
• Acute kidney injury or single functioning kidney
• Suspected complicated obstruction 1

Outpatient Management

• Adequate pain control with analgesics (preferably NSAID like diclofenac)
• Ability to maintain oral hydration
• No signs of infection or complications
• Follow-up arranged within 1-2 weeks 1

Common Pitfalls to Avoid

1. Diagnostic anchoring on nephrolithiasis - Always consider alternative diagnoses, especially with negative hematuria or atypical presentation 4

2. Missing dangerous mimics - Consider leaking abdominal aortic aneurysm in older patients, ectopic pregnancy in women of childbearing age 1

3. Relying solely on ultrasound - While useful as an initial screening tool, ultrasound alone may miss ureteral stones and other important pathology 1

4. Delaying imaging in moderate to severe pain - Non-contrast CT provides rapid, accurate diagnosis and should not be delayed in patients with significant symptoms 5

5. Overlooking pyonephrosis - Infected hydronephrosis is a urological emergency requiring prompt drainage; consider this diagnosis in patients with fever and hydronephrosis 1

By following this systematic approach to the workup of flank pain, clinicians can efficiently diagnose urolithiasis while identifying alternative diagnoses and complications that require specific management.