What is the initial assessment for a person presenting with acute flank pain?

Initial Assessment for Acute Flank Pain

The initial assessment for a patient with acute flank pain should include a focused history, targeted physical examination, urinalysis, and appropriate imaging with non-contrast CT scan as the gold standard for suspected urolithiasis. 1

History Taking

• Timing and onset of pain (abrupt onset suggests renal colic) 1
• Pain characteristics:
  • Location (unilateral flank pain radiating to groin/genitals is classic for renal colic) 1
  • Severity (typically severe in renal colic)
  • Radiation pattern (to groin or genitals in urolithiasis)
• Associated symptoms:
  • Nausea/vomiting
  • Fever (suggests infection)
  • Hematuria (visible or reported)
  • Lower urinary tract symptoms (frequency, urgency, dysuria)
• Past medical history:
  • Previous kidney stones
  • Recent urinary tract infections
  • Urological conditions
• Risk factors for alternative diagnoses:
  • Age >60 years (consider abdominal aortic aneurysm) 1
  • Women with delayed menses (consider ectopic pregnancy) 1

Physical Examination

• Vital signs (pulse, blood pressure, temperature) to exclude shock and systemic infection 1
• Abdominal examination:
  • Site of maximal tenderness
  • Signs of peritonitis (rebound tenderness, guarding)
  • Costovertebral angle tenderness (positive in pyelonephritis and renal colic)
  • Palpation for abdominal masses
• Genital examination when appropriate

Laboratory Tests

• Urinalysis:
  • Hematuria supports diagnosis of urolithiasis (present in >80% of cases) 1
  • Pyuria and bacteriuria suggest infection
  • Proteinuria may indicate glomerular disease
• Complete blood count:
  • Leukocytosis suggests infection
• Basic metabolic panel:
  • Assess renal function
  • Electrolyte abnormalities

Imaging Studies

• Non-contrast CT abdomen and pelvis:

  • Gold standard for urolithiasis with 97% sensitivity 1
  • Can identify stone location, size, and complications
  • Can diagnose alternative causes of flank pain 2
  • Should be performed within 7 days of symptom onset 1

• Ultrasound (alternative or complementary):

  • Less sensitive than CT for stone detection (24-57%) 1
  • Highly sensitive (up to 100%) for hydronephrosis 1
  • Preferred initial test in pregnant patients 1
  • Addition of color Doppler improves sensitivity for small stones 1

Management Decision Algorithm

1. Assess pain severity and vital signs

   • If shock, fever >38°C, or peritoneal signs: immediate hospital admission 1
   • If stable: proceed with assessment

2. Provide analgesia

   • Intramuscular diclofenac 75mg preferred (if not contraindicated) 1
   • Alternative: opioid with antiemetic if NSAIDs contraindicated

3. Evaluate response to analgesia

   • If pain not relieved within 1 hour: arrange immediate hospital admission 1
   • If pain relieved: continue outpatient management

4. Arrange appropriate imaging

   • Non-contrast CT for most patients
   • Ultrasound for pregnant patients or those with contraindications to CT

5. Follow-up

   • Phone call 1 hour after initial assessment 1
   • Instruct patient to strain urine to catch any passed stones
   • Encourage fluid intake

Common Pitfalls and Caveats

• Not considering dangerous alternative diagnoses:

  • Abdominal aortic aneurysm in older patients
  • Ectopic pregnancy in women of childbearing age
  • Pyelonephritis (can present with similar symptoms) 3
  • Renal cell carcinoma (rare but important consideration) 4

• Relying solely on presence/absence of hematuria:

  • Absence of hematuria does not rule out urolithiasis
  • Hematuria can be present in other conditions

• Delaying imaging:

  • Early imaging is crucial for accurate diagnosis and management planning
  • Secondary signs of obstruction may not develop within first 2 hours 1

• Inadequate pain control:

  • Failure to provide adequate analgesia can lead to unnecessary suffering
  • Reassess pain control regularly

By following this systematic approach to the assessment of acute flank pain, clinicians can efficiently diagnose urolithiasis while identifying alternative diagnoses that may require different management strategies.