What laboratory tests are recommended for a patient presenting with dizziness?

Laboratory Work-Up for Dizziness

For patients presenting with dizziness, laboratory testing should include serum glucose, electrolytes (particularly sodium), complete blood count, renal function tests, thyroid-stimulating hormone, and pregnancy testing in women of childbearing age. 1

Initial Assessment and Classification

Before ordering laboratory tests, it's important to classify the type of dizziness:

• Vertigo: Sensation of spinning or movement
• Presyncope: Feeling of impending faint
• Disequilibrium: Unsteadiness when walking
• Lightheadedness: Vague sensation of being disconnected

Recommended Laboratory Tests

Core Laboratory Tests

• Serum glucose: Essential for all patients with dizziness as hypoglycemia can present with dizziness 1, 2
• Electrolytes (including sodium, calcium, and magnesium): Particularly important to detect hyponatremia 3, 1
• Complete blood count: To evaluate for anemia 3
• Blood urea nitrogen and creatinine: To assess renal function 3
• Thyroid-stimulating hormone: To rule out thyroid dysfunction 3
• Pregnancy test: For women of childbearing age 3, 1

Additional Tests Based on Clinical Presentation

• Liver function tests: Particularly in patients with suspected alcohol-related issues or medication side effects 3
• Drug levels: When medication toxicity is suspected
• Drug screen: Consider in patients with new-onset dizziness without clear etiology 3

Evidence-Based Approach

The American College of Emergency Physicians guidelines indicate that laboratory testing is of very low yield in patients with new-onset dizziness who have returned to baseline 3, 1. However, glucose abnormalities and hyponatremia are the most frequent abnormalities identified and should be evaluated 3.

Studies have shown that:

• Hypoglycemia is occasionally found unexpectedly in patients with dizziness 3
• Hyponatremia may be present in patients with psychogenic water ingestion 3
• Hypocalcemia is rarely found in otherwise healthy patients 3

Special Considerations

1. Patients with known medical disorders: More extensive testing may be needed for patients with renal insufficiency, malnutrition, or those taking diuretics 3, 1

2. Acute Vestibular Syndrome: For patients with continuous vertigo, nausea/vomiting, and nystagmus, the HINTS examination is more valuable than laboratory testing for distinguishing between benign peripheral causes and potentially life-threatening central causes 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

When to Consider Imaging Instead of Laboratory Tests

MRI is recommended for:

• Acute Vestibular Syndrome with abnormal HINTS exam
• Presence of neurological deficits
• High vascular risk patients with Acute Vestibular Syndrome even with normal exam 1

CT has low yield (<1%) in isolated dizziness without neurological deficits 1.

Common Pitfalls to Avoid

1. Over-reliance on laboratory testing: History and physical examination predict the majority of patients who will have laboratory abnormalities 3

2. Missing central causes: Don't rely solely on laboratory tests to rule out serious central causes of dizziness

3. Ignoring medication effects: Many medications can cause dizziness; always review the patient's medication list

4. Assuming all dizziness is benign: Posterior circulation stroke can present with isolated dizziness 1

5. Unnecessary extensive testing: Routine testing of calcium, magnesium, or phosphate levels is not supported by evidence in otherwise healthy patients 3