Laboratory Testing for Nausea and Vomiting
Order a basic metabolic panel (electrolytes, glucose, BUN, creatinine), complete blood count, liver function tests (AST, ALT, bilirubin), lipase, and urinalysis as the initial laboratory workup for any patient presenting with new-onset nausea and vomiting. 1
Initial Laboratory Panel
The following tests should be obtained to exclude metabolic causes and assess for dehydration:
- Complete blood count (CBC) – identifies infection, anemia, or hematologic abnormalities 1
- Serum electrolytes – detects hypokalemia, hypochloremia, and metabolic alkalosis from prolonged vomiting 1
- Glucose – rules out hypoglycemia or hyperglycemia (diabetic ketoacidosis) 1, 2
- Liver function tests (AST, ALT, bilirubin) – evaluates hepatobiliary pathology 1
- Lipase – screens for pancreatitis 1
- BUN and creatinine – assesses renal function and dehydration status 1
- Urinalysis – identifies urinary tract infection, ketones, or renal disease 1, 2
Additional Testing Based on Clinical Context
Pregnancy and Reproductive Age
- Urine or serum pregnancy test – mandatory in all females of reproductive age, as pregnancy is a common cause 3, 2
Suspected Toxin or Substance Use
- Urine drug screen – particularly important in adolescents and young adults to assess for cannabis use (Cannabis Hyperemesis Syndrome) or other substances 1
Endocrine and Metabolic Causes (When Clinically Indicated)
- Serum calcium – hypercalcemia causes nausea and vomiting 1, 4
- Thyroid-stimulating hormone (TSH) – hypothyroidism can present with GI symptoms 1, 2
- Morning cortisol or ACTH stimulation test – if Addison's disease is suspected 1
Infectious Considerations
- Stool studies with cultures – if infectious diarrhea accompanies vomiting 2
- COVID-19 testing – in high-prevalence settings, as GI symptoms may precede respiratory symptoms by several days 5
Pediatric-Specific Considerations
In children with vomiting and dehydration or red flag signs (bilious vomiting, altered mental status, severe dehydration), obtain:
- Serum electrolytes and blood gases – to identify metabolic derangements 6
- Renal and liver function tests – to diagnose systemic causes 6
- Blood glucose – symptomatic hypoglycemia requires urgent treatment 6
Critical Pitfalls to Avoid
- Never delay imaging if bilious vomiting is present – this represents a surgical emergency (malrotation with volvulus, obstruction) requiring immediate fluoroscopy or upper GI series, not just laboratory testing 4
- Do not overlook electrolyte correction – hypokalemia and hypomagnesemia from prolonged vomiting require aggressive replacement 1
- Monitor for QTc prolongation – especially when using ondansetron in patients with electrolyte abnormalities 1
- Avoid stigmatizing cannabis users – obtain a thorough substance use history in a non-judgmental manner, as Cannabis Hyperemesis Syndrome is increasingly common 1, 4
When to Proceed Beyond Laboratory Testing
If initial laboratory tests are normal but symptoms persist beyond 7 days or worsen:
- Upper endoscopy (EGD) – to exclude mechanical obstruction, peptic ulcer disease, or malignancy 1, 4
- Gastric emptying scintigraphy – if gastroparesis is suspected 4
- Head CT – if intracranial process is suspected based on neurologic signs 4, 2
The extent of laboratory investigation should be tailored to symptom severity, duration (acute vs. chronic), and presence of alarm features (bilious vomiting, severe dehydration, altered mental status, abdominal distension). 7, 2, 8