What laboratory tests are needed to evaluate acute nausea and vomiting?

Laboratory Tests for Evaluating Acute Nausea and Vomiting

For patients presenting with acute nausea and vomiting, a complete blood count (CBC), comprehensive metabolic panel (including electrolytes, glucose, liver and renal function tests), and C-reactive protein (CRP) should be performed as the initial laboratory evaluation. 1

Essential Laboratory Tests

• Complete blood count (CBC) - To assess for infection, anemia, or other hematologic abnormalities 1
• Comprehensive metabolic panel - To evaluate:
  • Electrolytes (sodium, potassium, chloride) - Detect imbalances from dehydration 1
  • Blood glucose - Identify hypoglycemia or hyperglycemia 1
  • Renal function (BUN, creatinine) - Assess for dehydration or renal impairment 1
  • Liver function tests (AST, ALT, bilirubin) - Detect hepatic involvement 1
• C-reactive protein (CRP) - To assess for inflammatory processes 1
• Blood gas analysis - For base excess and lactate levels to evaluate acid-base status and tissue perfusion 1
• Urinalysis - To check for ketones, infection, and assess hydration status 2
• Pregnancy test - For women of childbearing age to rule out pregnancy-related nausea 2

Additional Tests Based on Clinical Presentation

• Amylase and lipase - If pancreatitis is suspected 2
• Thyroid-stimulating hormone (TSH) - If thyroid dysfunction is suspected 2
• Stool studies with cultures - When infectious gastroenteritis is suspected 2

Imaging Studies When Indicated

• Plain radiographs (neck, chest, abdomen) - To assess for radiopaque foreign bodies, obstruction, or perforation 1
• Computed tomography (CT) - When complications such as perforation, abscess, or other serious conditions are suspected 1
• CT of the head - If an intracranial process is suspected as the cause of vomiting 2

Laboratory Evaluation Algorithm

1. Initial assessment: Evaluate hydration status and presence of alarm symptoms (bilious vomiting, hematemesis, altered mental status) 3

2. For uncomplicated acute nausea/vomiting (likely viral or self-limited):

   • CBC, electrolytes, renal function tests 1
   • Pregnancy test in women of childbearing age 2

3. For moderate to severe symptoms or concerning features:

   • Complete metabolic panel including liver function tests 1
   • CRP and blood gas analysis 1
   • Consider imaging based on clinical suspicion 1

4. For persistent symptoms (>7 days):

   • Expand laboratory evaluation to include TSH, amylase/lipase 2
   • Consider specialty-specific testing based on suspected etiology 4

Important Considerations

• Laboratory abnormalities typically resolve with hydration and resolution of vomiting in simple cases 1
• Persistent laboratory abnormalities despite symptom resolution should prompt investigation for another etiology 1
• Contrast studies are not recommended in the acute setting and should not delay other investigations 1
• When evaluating patients with chemotherapy-related nausea and vomiting, the same initial laboratory tests apply, with additional monitoring for specific medication effects 1

Remember that laboratory testing should be guided by the clinical presentation, and not all tests are necessary for every patient with acute nausea and vomiting 4, 2.