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

Laboratory Evaluation for 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. 1

First-Line Laboratory Tests

• Complete Blood Count (CBC)

  • Evaluates for leukocytosis (may indicate infection, inflammation)
  • Assesses for anemia (may indicate GI bleeding)
  • Hemoconcentration may be present with significant fluid losses

• Comprehensive Metabolic Panel (CMP)

  • Electrolytes: Identifies dehydration and metabolic derangements from vomiting
  • Glucose: Rules out diabetic emergencies
  • BUN/Creatinine: Assesses renal function and dehydration status
  • Liver enzymes: Evaluates for hepatobiliary disease

• Liver Function Tests

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

• Lipase

  • More specific than amylase for pancreatic inflammation
  • Critical for diagnosing pancreatitis

• Urinalysis

  • Rules out urinary tract infection
  • Assesses hydration status
  • May identify ketones in diabetic emergencies

Additional Tests Based on Clinical Suspicion

• Lactate

  • Elevated levels (>2 mmol/L) may indicate intestinal ischemia
  • Sensitivity of 60% and specificity of 82% for intestinal ischemia 1
  • Should not be overlooked as it may be the only early laboratory indicator of intestinal ischemia

• D-dimer

  • Consider if mesenteric ischemia is suspected
  • Elevated in intestinal ischemia with similar sensitivity and specificity as lactate 1

• Pregnancy test

  • Essential for women of childbearing age
  • Rules out pregnancy-related conditions 1

• Thyroid function tests

  • Consider if hypothyroidism is suspected as a cause of ileus 1

Important Clinical Considerations

• Laboratory values should be interpreted in the context of the patient's clinical presentation, as normal lab values do not exclude serious pathology, especially early in the disease course 1

• Electrolyte abnormalities from vomiting require careful attention as they can cause significant metabolic disturbances

• Laboratory tests may need to be repeated as values can change rapidly in acute abdominal conditions

• Laboratory testing should complement, not replace, appropriate imaging studies when indicated 1

Common Pitfalls to Avoid

1. Relying solely on normal laboratory values to exclude serious pathology, especially early in presentation

2. Failing to repeat laboratory tests in patients with ongoing symptoms or clinical deterioration

3. Overlooking elevated lactate levels, which may be the only early indicator of intestinal ischemia

4. Delaying appropriate imaging studies while waiting for laboratory results in patients with concerning clinical presentations

5. Not considering pregnancy in women of childbearing age, which can significantly alter management

Remember that laboratory testing is just one component of the evaluation. The clinical presentation, physical examination findings, and appropriate imaging studies are equally important in determining the etiology of abdominal pain and vomiting.