What is the best approach to managing abdominal pain and determining its underlying cause?

Systematic Approach to Abdominal Pain Evaluation

The optimal management of abdominal pain requires a structured clinical assessment prioritizing vital signs and alarm features, followed by pain location-guided imaging—specifically CT abdomen/pelvis with IV contrast for nonlocalized pain, ultrasound for right upper quadrant pain, and targeted laboratory testing including mandatory pregnancy testing in women of childbearing age. 1

Initial Clinical Assessment: Identify Life-Threatening Conditions First

Vital Signs as Early Warning System

• Tachycardia is the single most sensitive early warning sign of surgical complications and should trigger urgent investigation even before other symptoms develop 1
• The combination of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 2, 1
• Hypotension with hypoperfusion signs (oliguria, altered mental status, lactic acidosis) indicates ongoing organ failure requiring immediate intervention 2

Red Flag Features Requiring Urgent Evaluation

• Pain out of proportion to physical examination findings strongly suggests mesenteric ischemia (30-90% mortality) and requires immediate CT angiography 1, 3
• Signs of peritonitis (rigid abdomen, rebound tenderness, guarding) indicate perforation or advanced infection requiring emergent surgical consultation 2, 1
• Abdominal distension with vomiting suggests bowel obstruction 1
• Sudden onset severe pain may indicate aortic dissection or ruptured aneurysm 3

Pain Characterization: Use Quality and Location as Diagnostic Framework

Pain Quality Differentiation

• Visceral pain (deep, pressure-like, poorly localized) suggests hollow organ distension, inflammation, or ischemia 4
• Parietal/somatic pain (sharp, well-localized, worsened by movement) indicates peritoneal irritation or abdominal wall involvement 4
• This distinction guides the urgency of evaluation and likelihood of surgical pathology 4

Location-Based Differential Diagnosis

The American College of Radiology provides specific imaging recommendations based on pain location 2, 1:

Right Upper Quadrant:

• Ultrasound is the initial imaging of choice for suspected biliary disease 1, 5
• Obtain liver function tests (ALT, AST, alkaline phosphatase, bilirubin) 5

Right Lower Quadrant:

• Ultrasound is the most appropriate initial imaging method 1
• CT abdomen/pelvis with contrast if ultrasound is inconclusive or for suspected appendicitis in adults 1
• Complete blood count with differential to assess for appendicitis 5

Left Lower Quadrant:

• CT abdomen/pelvis with contrast is recommended, especially for suspected diverticulitis 1

Nonlocalized/Diffuse Pain:

• CT abdomen/pelvis with IV contrast is the optimal imaging choice, particularly with fever or suspicion of serious illness 2, 1
• This approach has the broadest diagnostic capability and changes management in 49% of cases, alters admission status in 24%, and modifies surgical plans in 25% 2

Essential Laboratory Testing

Mandatory Initial Tests

• Complete blood count to evaluate for leukocytosis (infection/inflammation) 1, 5
• Beta-hCG testing is mandatory in ALL women of childbearing age before imaging to rule out ectopic pregnancy 1, 5
• Comprehensive metabolic panel including liver function tests 5
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 5
• Serum lipase (more specific than amylase for pancreatitis) 5

Advanced Laboratory Testing Based on Clinical Suspicion

• Elevated lactate suggests ischemia or sepsis, though normal levels do not exclude early ischemia or internal herniation 1
• C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease 1
• D-dimer and lactate if mesenteric ischemia is suspected 1, 5
• Blood cultures if fever present and sepsis suspected 5

Imaging Strategy: Avoid Radiation When Possible, But Don't Delay Diagnosis

CT Abdomen/Pelvis with IV Contrast

• This is the preferred imaging for nonlocalized acute abdominal pain with fever or concerning features 2, 1, 3
• IV contrast increases the spectrum of detectable pathology compared to non-contrast studies 2
• Many institutions no longer routinely use oral contrast due to delays in acquisition without clear diagnostic advantage 2
• Changes leading diagnosis in 49% of emergency department patients with nontraumatic abdominal complaints 2

Ultrasound Applications

• First-line for right upper quadrant pain (biliary pathology) 1, 5
• Initial imaging for right lower quadrant pain before CT 1
• Preferred in pregnant patients when available 2
• Consider staged algorithms using ultrasound first, followed by CT if inconclusive 2

MRI Considerations

• Not routinely available in emergency settings 2
• Useful in pregnant patients with abdominal pain when ultrasound is inconclusive 2
• For acute appendicitis, MRI has 94% sensitivity and 96% specificity 2

Diagnostic Laparoscopy

• When imaging has been unhelpful, diagnostic laparoscopy provides definitive diagnosis in 86-100% of cases 2
• Allows simultaneous therapeutic intervention 2

Special Population Considerations

Elderly Patients

• Symptoms may be atypical even with serious pathology 1
• Higher likelihood of malignancy, diverticulitis, and vascular causes 1
• Require more thorough evaluation even if laboratory tests are normal 2
• Advanced age combined with high disease severity and sepsis carries very high mortality risk 2

Women of Childbearing Age

• Always consider gynecologic conditions: ectopic pregnancy, ovarian torsion, pelvic inflammatory disease 1, 6
• Mandatory pregnancy testing before any imaging 1, 5
• CT abdomen/pelvis with contrast is most appropriate for pelvic pain 1

Post-Bariatric Surgery Patients

• Often present with atypical symptoms 1
• Tachycardia is the most critical warning sign 1
• Classic peritoneal signs often absent 1
• Consider internal herniation even with normal lactate 1

Immunocompromised Patients

• Typical signs of abdominal sepsis may be masked 2
• Diagnosis may be delayed with high mortality rates 2
• More extensive workup necessary 5

Common Pitfalls to Avoid

• Do not rely on conventional radiography—it has limited diagnostic value for most causes of abdominal pain and should not be routinely ordered 2, 5
• Do not assume normal vital signs exclude serious pathology, especially in elderly or immunocompromised patients 2, 1
• Do not delay imaging in patients with concerning features while waiting for laboratory results 2
• Do not miss the "window of opportunity"—delays beyond 24 hours in intervention convert low-risk patients to high-risk 2
• Do not overlook tachycardia as an isolated finding, particularly in post-surgical or post-bariatric patients 1
• Failing to obtain pregnancy testing before imaging can lead to delayed diagnosis of life-threatening ectopic pregnancy 5

When Palliative Care Should Be Discussed

When patients present with an accumulated number of risk factors—including advanced age, high disease severity, and sepsis or septic shock—they have a very high risk of death, and palliative care should be actively discussed when operative treatment appears futile 2