What is the initial work-up, including labs and testing, for a patient presenting with abdominal pain?

Initial Work-Up for Abdominal Pain

Begin with vital signs assessment and targeted laboratory testing including CBC, comprehensive metabolic panel, urinalysis, serum lipase, and mandatory β-hCG in all women of reproductive age, followed by location-specific imaging with ultrasound for right upper quadrant pain and CT with contrast for lower quadrant or diffuse pain. 1, 2

Immediate Clinical Assessment

Vital Signs - Critical Warning Indicators

• 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 1
• Hypotension or tachypnea may indicate bleeding or other life-threatening complications 1

Pain Characteristics That Demand Urgent Action

• Abrupt or instantaneous onset of severe pain suggests vascular catastrophe (aortic dissection or mesenteric ischemia) 1
• Pain out of proportion to physical examination findings should be assumed to be acute mesenteric ischemia until disproven 1
• Ripping, tearing, stabbing, or sharp quality pain suggests aortic dissection 1

Physical Examination Red Flags

• Rebound tenderness, rigid abdomen, or positive Murphy's sign require urgent evaluation 1
• Asymmetric gaseous distention with emptiness of the left iliac fossa is pathognomonic for sigmoid volvulus 1
• Resonant liver percussion note indicates pneumoperitoneum and requires immediate imaging 3
• Classic peritoneal signs are often absent in post-bariatric surgery patients and elderly patients - do not rely on their absence to rule out serious pathology 1

Mandatory Laboratory Testing

Initial Panel for All Patients

• Complete blood count (CBC) to evaluate for leukocytosis suggesting infection or inflammation 1, 2
• Comprehensive metabolic panel (CMP) including liver function tests (ALT, AST, alkaline phosphatase, bilirubin) to evaluate hepatobiliary pathology and organ function 2
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 2
• Serum lipase (more specific than amylase for pancreatitis) 2
• β-hCG testing is mandatory in all women of reproductive age before any imaging to rule out ectopic pregnancy 1, 2

Additional Labs Based on Clinical Suspicion

• C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease, though normal CRP does not exclude complications 1
• Elevated lactate suggests ischemia or sepsis, but normal levels do not exclude internal herniation or early ischemia 1
• Procalcitonin is helpful for assessing inflammatory response in suspected sepsis 1
• D-dimer and lactate levels if mesenteric ischemia is suspected 1
• Blood cultures if fever is present and sepsis is suspected 2

Imaging Strategy Based on Pain Location

Right Upper Quadrant Pain

• Abdominal ultrasound is the most appropriate initial imaging method 1, 2
• Particularly useful for evaluating acute cholecystitis 1

Right Lower Quadrant Pain

• Abdominal ultrasound is the most appropriate initial imaging method 1
• Consider ultrasound before proceeding to CT to minimize radiation exposure, especially in young patients 1
• CT of abdomen and pelvis with contrast if ultrasound is inconclusive 1

Left Lower Quadrant Pain

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

Pelvic Pain

• CT of abdomen and pelvis with contrast is the most appropriate initial imaging method 1

Diffuse or Non-Specific Abdominal Pain

• CT of abdomen and pelvis with contrast is the optimal choice, especially if there is fever or suspicion of serious illness 1
• Conventional radiography has limited diagnostic value (49% sensitivity for bowel obstruction) and should not be routinely ordered 1, 2, 3

Epigastric Pain

• Consider upper GI series with fluoroscopy if gastritis, peptic ulcer disease, or GERD is suspected 1

Imaging Based on Suspected Condition

• Acute appendicitis: CT of abdomen and pelvis with contrast 1
• Kidney stones: Non-contrast CT of abdomen and pelvis 1
• Bowel obstruction: CT of abdomen and pelvis with contrast 1
• Mesenteric ischemia: CT angiography of the abdomen 1
• Suspected perforation: CT is most sensitive (89% sensitivity) for detecting pneumoperitoneum and can identify the perforation site 3

Special Population Considerations

Women of Childbearing Age

• Always consider gynecologic conditions including ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease 1
• β-hCG testing is mandatory before imaging 1, 2

Elderly Patients

• Symptoms may be atypical and require more thorough evaluation even if laboratory tests are normal 1
• Higher likelihood of malignancy, diverticulitis, and vascular causes 1
• Do not over-rely on normal laboratory values early in disease - many tests are nonspecific and may be normal despite serious infection 1

Post-Bariatric Surgery Patients

• Tachycardia is the most critical warning sign - often present with atypical symptoms 1
• Classic peritoneal signs are often absent 1
• Internal herniation should be considered even with normal lactate 1

Immunocompromised Patients

• May have masked signs of abdominal sepsis with delayed diagnosis and high mortality 1
• More extensive workup may be necessary 2

Critical Pitfalls to Avoid

• Failing to obtain pregnancy testing in women of reproductive age before imaging can lead to delayed diagnosis of ectopic pregnancy 2
• Normal laboratory values do not exclude serious pathology, especially in elderly patients 1
• Absence of peritoneal signs does not exclude bowel ischemia - patients with sigmoid volvulus often lack peritoneal signs despite established ischemia 1
• Avoid overuse of CT scans to minimize ionizing radiation exposure, especially in young patients 1
• Do not routinely order plain radiographs - they have limited diagnostic value except for detecting pneumoperitoneum 1, 2, 3