What labs should I order for a patient presenting with abdominal pain?

Laboratory Tests for Abdominal Pain Evaluation

For patients presenting with abdominal pain, a comprehensive laboratory workup should include complete blood count, comprehensive metabolic panel, urinalysis, and lipase, with additional tests guided by the specific clinical presentation and suspected diagnosis. 1, 2

Initial Laboratory Evaluation

Core Laboratory Tests

• Complete blood count (CBC): Evaluates for leukocytosis (infection/inflammation), anemia (GI bleeding)
• Comprehensive metabolic panel (CMP): Assesses liver function, kidney function, and electrolyte abnormalities
• Urinalysis: Screens for urinary tract infection, nephrolithiasis
• Lipase: Essential for evaluating suspected pancreatitis
• Pregnancy test: Required for all women of reproductive age 1

Location-Specific Laboratory Tests

Right Upper Quadrant Pain

• Liver function tests (AST, ALT, alkaline phosphatase, bilirubin)
• Hepatitis serologies if liver enzymes elevated

Right Lower Quadrant/Left Lower Quadrant Pain

• C-reactive protein (CRP): Inflammatory marker useful for appendicitis, diverticulitis
• Fecal calprotectin: Consider for suspected inflammatory bowel disease

Diffuse Abdominal Pain

• Lactate: Critical for suspected mesenteric ischemia 1
• D-dimer: May be elevated in mesenteric ischemia 1
• Blood cultures: For patients with fever or suspected sepsis

Specialized Testing Based on Clinical Suspicion

Suspected Biliary Disease

• Gamma-glutamyl transferase (GGT): More specific for biliary disease
• Coagulation studies (PT/INR): For jaundiced patients

Suspected Inflammatory Conditions

• Erythrocyte sedimentation rate (ESR): Non-specific inflammatory marker
• Stool studies: For suspected infectious gastroenteritis

Suspected Gynecologic Conditions

• Beta-hCG: Essential for ruling out ectopic pregnancy 1
• Cervical/vaginal swabs: For suspected pelvic inflammatory disease

Clinical Decision Algorithm

1. Assess hemodynamic stability

   • If unstable: Immediate resuscitation and expedited imaging

2. Determine pain location

   • Right upper quadrant: CBC, CMP, lipase, LFTs
   • Right lower quadrant: CBC, CMP, urinalysis, CRP, pregnancy test in women
   • Left lower quadrant: CBC, CMP, urinalysis, CRP
   • Epigastric: CBC, CMP, lipase, cardiac enzymes
   • Diffuse: CBC, CMP, lipase, lactate, urinalysis

3. Consider special populations

   • Elderly patients: Lower threshold for comprehensive testing as they often present atypically 2
   • Immunocompromised: CBC with differential, blood cultures
   • Pregnant women: Avoid radiation exposure; beta-hCG essential 1

Important Considerations

• Laboratory tests alone are insufficient for diagnosing many causes of abdominal pain and should be interpreted alongside clinical findings and appropriate imaging 1
• In patients with suspected mesenteric ischemia, laboratory findings may include metabolic acidosis, elevated lactate, leukocytosis, and elevated D-dimer, but these are often late findings 1
• For patients with functional dyspepsia, the British Society of Gastroenterology recommends a full blood count for patients ≥55 years and coeliac serology for those with overlapping IBS-type symptoms 1

Common Pitfalls to Avoid

• Relying solely on laboratory tests: Many serious conditions may present with normal initial labs
• Delaying imaging when indicated: For suspected appendicitis, diverticulitis, or mesenteric ischemia, prompt imaging is crucial
• Forgetting pregnancy testing: Always perform beta-hCG testing in women of reproductive age 1
• Missing atypical presentations in elderly patients: Only 17% of elderly patients with acute diverticulitis present with fever, and 43% do not have leukocytosis 2

Remember that laboratory testing should be guided by clinical suspicion and used in conjunction with appropriate imaging studies to establish a definitive diagnosis for abdominal pain.