What lab workup is recommended for a patient presenting with abdominal pain?

Laboratory Workup for Abdominal Pain

The recommended laboratory workup for a patient presenting with abdominal pain should include complete blood count, comprehensive metabolic panel, urinalysis, lipase, and pregnancy testing in women of reproductive age, with additional tests guided by the suspected diagnosis based on pain location and clinical presentation. 1, 2

Initial Laboratory Evaluation

• Complete blood count (CBC) to assess for leukocytosis, which may indicate infection or inflammation 1, 2
• C-reactive protein (CRP) to evaluate for inflammatory processes 2
• Comprehensive metabolic panel including:
  • Electrolytes to assess fluid status and acid-base balance 2
  • Liver function tests (AST, ALT, bilirubin, alkaline phosphatase) for hepatobiliary pathology 1, 2
  • Creatinine and BUN to assess renal function 2
  • Glucose to rule out metabolic causes 2
• Urinalysis to evaluate for urinary tract infection or nephrolithiasis 1, 2
• Serum lipase for suspected pancreatitis (more specific than amylase) 1, 3
• Beta-human chorionic gonadotropin (β-hCG) testing in all women of reproductive age to rule out pregnancy-related conditions including ectopic pregnancy 1

Laboratory Tests Based on Location of Pain

Right Upper Quadrant Pain

• Liver function tests and hepatobiliary markers are particularly important 1
• Lipase if pancreatitis is suspected 1, 4

Right or Left Lower Quadrant Pain

• CBC with differential to assess for appendicitis or diverticulitis 1, 2
• CRP as an inflammatory marker 2

Diffuse Abdominal Pain

• Lactate and D-dimer if mesenteric ischemia is suspected 1
• Amylase and lipase if pancreatitis is suspected 4, 3

Special Considerations

• For suspected pancreatitis, lipase is preferred over amylase due to higher sensitivity (64% vs 50%) and similar specificity (97% vs 99%) 3
• Consider elevated cutoff levels (3-4 times the upper limit of normal) for pancreatic enzymes to improve diagnostic accuracy 4
• In patients with fever and abdominal pain, blood cultures should be considered, especially if sepsis is suspected 1
• For immunocompromised patients with abdominal pain, a more extensive workup may be necessary 1

Common Pitfalls to Avoid

• Relying solely on amylase for diagnosing pancreatitis - lipase is more specific and remains elevated longer 4, 3
• Failing to obtain pregnancy testing in women of reproductive age before proceeding with imaging studies 1
• Over-reliance on laboratory tests alone for diagnosis - laboratory findings early in the course of disease may be of little value in differentiating among causes of abdominal pain 1
• Repeating laboratory tests unnecessarily after a functional disorder diagnosis is established 5

When to Consider Additional Testing

• If initial laboratory workup is inconclusive but clinical suspicion remains high for serious pathology, imaging studies should be considered based on the location of pain 1
• For suspected mesenteric ischemia, additional markers such as lactate and D-dimer may be helpful, though they lack specificity 1
• In cases of persistent symptoms without clear diagnosis, consider referral to specialists and targeted testing based on the most likely diagnoses 5

Remember that laboratory tests should complement, not replace, thorough clinical assessment, and the choice of imaging studies should be guided by the location of pain and clinical suspicion of specific conditions 1.