What laboratory tests should be ordered for a patient presenting with dizziness?

Laboratory Tests for Dizziness Evaluation

For patients presenting with dizziness, essential laboratory tests include serum glucose, electrolytes (sodium, potassium, calcium, magnesium), complete blood count, renal function tests, and thyroid-stimulating hormone. 1

Core Laboratory Tests

• Serum glucose: Essential for all patients with dizziness as hypoglycemia can present with dizziness and is occasionally found unexpectedly 1
• Electrolytes panel:
  • Sodium (to detect hyponatremia, which is among the most frequent abnormalities in dizziness) 1
  • Potassium (especially important in patients on diuretics or cardiac medications)
  • Calcium and magnesium (particularly in patients with risk factors for electrolyte disturbances)
• Complete blood count: To evaluate for anemia or infection 1
• Renal function tests: Blood urea nitrogen (BUN) and creatinine 1
• Thyroid-stimulating hormone (TSH): To assess for thyroid dysfunction 1

Additional Tests Based on Clinical Suspicion

• Pregnancy test: For women of childbearing age 1
• Liver function tests: Consider in patients with suspected alcohol-related issues 1
• Drug screen: For patients with suspected medication side effects or unexplained dizziness 1

Important Clinical Considerations

Evidence-Based Approach

Laboratory testing is of very low yield in patients with new-onset dizziness who have returned to baseline 1. The American College of Emergency Physicians guidelines note that glucose abnormalities and hyponatremia are the most frequent abnormalities identified in dizziness evaluation 1.

When to Limit Testing

Routine testing of calcium, magnesium, or phosphate levels is not supported by evidence in otherwise healthy patients without specific risk factors 1. History and physical examination predict the majority of patients who will have laboratory abnormalities 1.

Beyond Laboratory Testing

It's crucial to recognize that laboratory tests have limitations in dizziness evaluation:

1. The HINTS exam (Head Impulse test, Nystagmus, Test of Skew) is more valuable than laboratory testing for distinguishing between benign peripheral causes and potentially life-threatening central causes of vertigo 1

2. For patients with Acute Vestibular Syndrome (continuous vertigo, nystagmus, nausea/vomiting), the HINTS exam has a sensitivity of 96.7% and specificity of 94.8% for detecting central causes when performed correctly 1

3. Posterior circulation stroke can present with isolated vertigo in up to 25% of cases, with prevalence increasing to 75% in high vascular risk cohorts 1

Common Pitfalls to Avoid

• Over-reliance on laboratory testing: This can lead to missing central causes of dizziness 1
• Unnecessary extensive testing: Not supported by evidence in otherwise healthy patients 1
• Neglecting physical examination: The HINTS exam and other physical examination techniques are often more valuable than laboratory tests in determining the cause of dizziness 1
• Failing to consider medication effects: Many medications can cause dizziness, and medication regimens should be assessed in all patients 2

Remember that laboratory testing plays a supportive role in dizziness evaluation, while history, timing patterns, and targeted physical examination remain the cornerstone of diagnosis.