What investigations should be sent to evaluate nausea in a female patient?

Investigations for Nausea in a 27-Year-Old Female

A pregnancy test is the single most critical initial investigation in any woman of childbearing age presenting with nausea, followed by a comprehensive metabolic panel, complete blood count, liver function tests, and urinalysis. 1, 2

Essential Initial Laboratory Workup

The American Gastroenterological Association recommends a standardized approach to evaluating nausea that prioritizes ruling out pregnancy and metabolic derangements first 1, 2:

Mandatory First-Line Tests

• Urine pregnancy test (β-hCG): This is non-negotiable in all women of childbearing age, as nausea affects 30-90% of pregnant women, typically beginning at 4-6 weeks gestation and peaking at 8-12 weeks 3. Elevated hCG levels are directly implicated in pregnancy-related nausea 3.

• Comprehensive metabolic panel: Evaluates electrolytes (sodium, potassium), blood glucose, renal function (BUN, creatinine), and identifies metabolic causes or consequences of vomiting 1, 2. This detects diabetic complications, hypoglycemia, pre-renal acute renal failure from dehydration, and electrolyte imbalances 1.

• Complete blood count (CBC): Assesses for infection, anemia, or hematologic abnormalities that may contribute to nausea 1, 2.

• Liver function tests (AST, ALT, bilirubin): Rules out hepatic causes of nausea 1, 2.

• Urinalysis: Evaluates hydration status, rules out urinary tract infection, and assesses for ketones (particularly important if cyclic vomiting syndrome is suspected) 1, 2.

Additional Testing Based on Clinical Red Flags

If Persistent or Severe Symptoms

• Serum lipase: Consider if abdominal pain accompanies nausea to rule out pancreatitis 2.

• Thyroid function tests: Evaluate if adrenal insufficiency (Addison's disease) is suspected based on clinical presentation 1, 2.

If Cyclic Pattern or Cannabis Use History

• Document cannabis use patterns: Prolonged use (>1 year) may indicate cannabinoid hyperemesis syndrome rather than cyclic vomiting syndrome 1, 2.

• Basic workup for cyclic vomiting syndrome: CBC, electrolytes, glucose, liver function tests, lipase, and urinalysis with assessment for ketones 1.

If Obstructive Symptoms Present

• Abdominal radiography or CT scan: Only if clinical examination suggests bowel obstruction (abdominal distention, absent bowel sounds, severe cramping pain) 1, 2.

Critical Pitfalls to Avoid

Do not order gastric emptying studies during acute nausea or vomiting episodes—results will be uninterpretable 1. These should only be considered for suspected gastroparesis after symptoms have resolved and only if clinically indicated.

Avoid repeated endoscopic or imaging studies unless there is a documented change in clinical status 1. The evidence does not support routine upper endoscopy in young patients with isolated nausea without alarm features (weight loss, dysphagia, bleeding, anemia) 4.

Practical Clinical Algorithm

1. Immediate: Urine pregnancy test + comprehensive metabolic panel + CBC 1, 2
2. Same visit: Liver function tests + urinalysis 1, 2
3. If pregnancy positive: No further workup needed initially—this explains the nausea in most cases 3
4. If pregnancy negative and basic labs normal: Consider medication review, dietary triggers (lactose, fructose intolerance), and psychosocial factors before pursuing extensive additional testing 4
5. If alarm features present (weight loss >5%, severe dehydration, neurologic symptoms): Escalate to imaging and specialist consultation 2

The key principle is that symptoms alone are poor predictors of pathological versus functional illness 4, so the extent of investigation must be tailored based on the severity of presentation, presence of alarm features, and initial laboratory results rather than pursuing exhaustive testing in all patients.