What initial investigations should be sent for a patient presenting with abdominal pain?

Initial Investigations for Abdominal Pain

For patients presenting with abdominal pain, the initial investigations should include laboratory tests (complete blood count, electrolytes, liver enzymes, inflammatory markers) followed by imaging tailored to the location of pain, with ultrasound recommended for right upper quadrant pain and CT with contrast for diffuse or lower quadrant pain. 1

Laboratory Investigations

• Essential baseline tests:
  • Complete blood count (CBC)
  • Electrolytes
  • Liver function tests (ALT, AST, alkaline phosphatase, bilirubin)
  • Inflammatory markers (CRP, ESR)
  • Serum albumin
  • Pregnancy test for all women of reproductive age 1, 2
  • Urinalysis 2
  • Lipase (to evaluate for pancreatitis) 2

Imaging Based on Pain Location

Right Upper Quadrant Pain

• First-line: Ultrasonography 3, 1
  • High sensitivity (81%) and specificity (83%) for cholecystitis 3
  • No radiation exposure
  • Cost-effective and readily available in most settings 1
• Second-line (if ultrasound is equivocal):
  • CT with contrast 1
  • HIDA scan (96% sensitivity, 90% specificity for cholecystitis) 3
  • MRI (sensitivity 85%, specificity 81%) 3

Right Lower Quadrant Pain (Suspected Appendicitis)

• First-line: CT with IV contrast 1
  • Sensitivity of 94% for appendicitis (vs. 76% for ultrasound) 4
• Alternative: Ultrasound (for pregnant patients, young women, or when CT unavailable) 1

Left Lower Quadrant Pain (Suspected Diverticulitis)

• First-line: CT with IV contrast 3
  • Conditional recommendation, very low certainty of evidence 3
  • Superior sensitivity (81% vs. 61% for ultrasound) 4
• Alternative: Ultrasound or MRI if CT unavailable or contraindicated 3

Diffuse/Non-localized Abdominal Pain

• First-line: CT with IV contrast 3, 1
  • Provides comprehensive evaluation of multiple potential causes
  • Particularly valuable when clinical diagnosis is uncertain 3
• Alternative: Plain radiographs if CT not immediately available, though sensitivity is limited 3

Special Considerations

Suspected Intra-abdominal Abscess

• Adults: CT scan as initial diagnostic imaging modality 3
  • Use of IV contrast improves visualization of abscess wall 3
• Children: Ultrasound as initial diagnostic imaging modality 3
  • MRI is a reasonable alternative 3

Pregnant Patients

• For suspected cholecystitis or cholangitis: Ultrasound or MRI (no clear recommendation for one over the other) 3
• For suspected diverticulitis: Ultrasound or MRI (no clear recommendation for one over the other) 3

Elderly Patients

• Lower threshold for advanced imaging as signs and symptoms may be atypical 5
• Laboratory findings may be normal despite serious infection 3

Common Pitfalls to Avoid

• Dismissing pain as functional without adequate workup
• Administering antibiotics without evidence of infection
• Delaying imaging in patients with significant pain
• Failing to consider extra-abdominal causes of pain
• Relying solely on laboratory tests without appropriate imaging 1
• Overlooking gynecological causes in women 1

By following this evidence-based approach to investigating abdominal pain, clinicians can efficiently diagnose the underlying cause and initiate appropriate treatment, ultimately improving patient outcomes in terms of morbidity and mortality.