What labs and treatments are indicated for a patient presenting with nausea and retching?

Laboratory Evaluation for Nausea and Retching

For any patient presenting with nausea and retching, obtain complete blood count, serum electrolytes, glucose, liver function tests, lipase, and urinalysis to exclude metabolic causes and assess for dehydration. 1

Essential Initial Laboratory Tests

The following labs should be ordered immediately:

• Complete blood count (CBC) - to assess for infection or anemia 1
• Comprehensive metabolic panel - including electrolytes (sodium, potassium, chloride, bicarbonate), glucose, BUN, creatinine 1
• Liver function tests - AST, ALT, alkaline phosphatase, bilirubin 1
• Serum lipase - to exclude pancreatitis 1
• Urinalysis - to assess for urinary tract infection or ketones 1

Additional Testing Based on Clinical Context

Consider these additional tests when clinically indicated:

• Serum calcium - hypercalcemia is a common metabolic cause of nausea and vomiting 1
• Thyroid-stimulating hormone (TSH) - to exclude hypothyroidism 1
• Morning cortisol or ACTH stimulation test - if Addison's disease is suspected 1
• Urine drug screen - particularly important in younger patients to assess for cannabis use, as Cannabis Hyperemesis Syndrome is increasingly common 1
• Pregnancy test (urine or serum β-hCG) - in all women of childbearing age

Critical Electrolyte Monitoring

Ensure adequate hydration with intravenous crystalloids if dehydration is present, and monitor for electrolyte abnormalities, correcting as needed. 2

• Prolonged vomiting and retching can cause hypokalemia, hypochloremia, and metabolic alkalosis 3
• Assess for thiamine deficiency and consider supplementation (200-300 mg daily) in cases of prolonged retching 2

Imaging Considerations

• Obtain one-time esophagogastroduodenoscopy (EGD) or upper GI imaging to exclude obstructive lesions 1
• Avoid repeated endoscopy or imaging studies unless new symptoms develop 1
• Consider abdominal imaging if bowel obstruction is suspected, but never use antiemetics in suspected mechanical bowel obstruction, as this can mask progressive ileus and gastric distension 1

Cannabis Hyperemesis Syndrome Screening

Cannabis use history is critical, particularly in younger patients, and Cannabis Hyperemesis Syndrome should be suspected if heavy cannabis use preceded symptom onset. 1

• Definitive diagnosis requires 6 months of cannabis cessation or at least 3 typical cycle lengths without vomiting 1
• Do not stigmatize patients with cannabis use, and offer abortive and prophylactic therapy even with ongoing use, as treatments can still be effective 1

Treatment Initiation Based on Laboratory Results

If Metabolic Abnormalities Are Identified:

• Correct hypercalcemia - this is a reversible cause of nausea and vomiting 1
• Treat dehydration - with IV fluids 1
• Address electrolyte imbalances - particularly hypokalemia and hypomagnesemia 3

Pharmacologic Management While Awaiting Results:

Initiate dopamine receptor antagonists titrated to maximum benefit and tolerance, such as metoclopramide (10-20 mg orally three to four times daily), prochlorperazine (5-10 mg every 6-8 hours), or haloperidol. 1, 2

• Consider adding ondansetron (8 mg sublingual/oral every 4-6 hours) if symptoms persist after 4 weeks 1, 2
• Monitor for QTc prolongation when using ondansetron, especially in combination with other QT-prolonging agents 1, 2
• Monitor for extrapyramidal symptoms with dopamine antagonists, particularly in young males 1

If Gastroparesis or Gastritis Is Suspected:

• Consider proton pump inhibitor or H2 receptor antagonist 1
• Continue metoclopramide as it promotes gastric emptying 1