What labs should be ordered for a patient presenting with abdominal pain and vomiting?

Laboratory Tests for Patients with Abdominal Pain and Vomiting

For patients presenting with abdominal pain and vomiting, a comprehensive laboratory panel should include complete blood count (CBC), comprehensive metabolic panel (CMP), liver function tests, lipase, and urinalysis as first-line investigations to assess for common etiologies and complications. 1

Initial Laboratory Evaluation

Essential First-Line Tests:

• Complete Blood Count (CBC)

  • Leukocytosis (>90% of patients with intestinal obstruction will have elevated WBC) 1
  • Hemoglobin/hematocrit (to assess for anemia or hemoconcentration)

• Comprehensive Metabolic Panel (CMP)

  • Electrolytes (sodium, potassium, chloride, bicarbonate)
  • BUN and creatinine (to assess renal function and dehydration)
  • Glucose (hypoglycemia may indicate severe illness)

• Liver Function Tests

  • AST, ALT, alkaline phosphatase, bilirubin 1
  • Abnormal in approximately 15% of patients with certain conditions like COVID-19 1

• Serum Lactate

  • Elevated levels (>2 mmol/L) may indicate intestinal ischemia 1
  • Important marker for bowel compromise and tissue hypoperfusion

• Lipase

  • To evaluate for pancreatitis

• Urinalysis

  • To rule out urinary tract infection or renal stone disease
  • May show evidence of dehydration

Second-Line Tests Based on Clinical Suspicion

• Coagulation Studies

  • PT/INR, PTT (especially if liver disease or bleeding is suspected)

• D-dimer

  • Elevated in intestinal ischemia (sensitivity 60%, specificity 82%) 1
  • Consider if mesenteric ischemia is suspected

• Thyroid Function Tests

  • If hypothyroidism is suspected as a cause of ileus 1

• Pregnancy Test

  • For women of childbearing age to rule out pregnancy-related conditions 1

• Inflammatory Markers

  • C-reactive protein (CRP)
  • Erythrocyte sedimentation rate (ESR)

Special Considerations

For Suspected Bowel Obstruction

• Elevated WBC count (>90% of patients)
• Metabolic acidosis with elevated lactate (88% of patients) 1
• Consider D-dimer if mesenteric ischemia is suspected 1

For Suspected Liver Involvement

• Comprehensive liver panel including AST, ALT, bilirubin, and alkaline phosphatase
• If abnormal, consider viral hepatitis serology 1

For Suspected Infection

• Blood cultures if sepsis is suspected
• If ascites is present, diagnostic paracentesis with cell count, culture, and albumin 1

Clinical Pitfalls to Avoid

1. Don't rely solely on laboratory tests - Normal lab values don't exclude serious pathology, especially early in the disease course

2. Don't miss electrolyte abnormalities - Vomiting can cause significant electrolyte disturbances and metabolic alkalosis

3. Don't overlook lactate - Elevated lactate may be the only early laboratory indicator of intestinal ischemia 1

4. Don't forget to repeat tests - Laboratory values may change rapidly in acute abdominal conditions

5. Don't delay imaging if indicated - Laboratory tests should complement, not replace, appropriate imaging studies for abdominal pain

Remember that laboratory tests should be interpreted in the context of the patient's clinical presentation, and no single test is sufficient to diagnose the cause of abdominal pain and vomiting. Abnormal laboratory findings should guide further diagnostic evaluation, including appropriate imaging studies.