What laboratory tests are recommended for evaluating dizziness?

Laboratory Tests for Evaluating Dizziness

Laboratory testing plays a limited role in the evaluation of dizziness, with most cases requiring careful history and physical examination rather than extensive laboratory workup. 1, 2

Classification of Dizziness

• Dizziness should be categorized based on timing and triggers rather than subjective descriptions, into four main types: vertigo, presyncope, disequilibrium, and lightheadedness 1, 3
• This classification helps determine appropriate diagnostic testing and management 1

Initial Laboratory Evaluation

• For nonspecific dizziness without vertigo, ataxia, or other neurologic deficits, laboratory testing should be targeted based on clinical suspicion rather than ordered routinely 4
• Common laboratory tests to consider include:
  • Complete blood count (CBC) - to evaluate for anemia, which can cause presyncope and lightheadedness 5
  • Glucose testing - to rule out hypoglycemia or hyperglycemia, particularly in patients with diabetes 5
  • Electrolytes - to identify imbalances that may cause dizziness, particularly in patients on diuretics or with renal disease 3
  • Thyroid function tests - when symptoms suggest thyroid dysfunction 3

When to Consider Additional Testing

• Orthostatic vital signs should be checked when presyncope is suspected, particularly in elderly patients or those on medications that can cause hypotension 1, 3
• Cardiac evaluation (ECG, Holter monitoring) should be considered when cardiac causes are suspected 3
• Specialized vestibular testing may be appropriate when peripheral vestibular disorders are suspected and bedside tests are inconclusive 6

Imaging Considerations

• Neuroimaging is generally not indicated for isolated dizziness without neurological deficits, with diagnostic yield of CT being very low (<1%) and MRI only slightly higher (4%) 4
• MRI should be considered when:
  • Neurological examination reveals focal deficits 7
  • HINTS examination suggests a central cause (normal head impulse test, direction-changing nystagmus, or skew deviation) 7
  • Symptoms persist despite appropriate treatment for peripheral causes 7

Common Pitfalls to Avoid

• Ordering extensive laboratory testing for all patients with dizziness, which has low diagnostic yield and increases healthcare costs 1, 2
• Relying solely on laboratory tests without performing appropriate bedside examinations such as the Dix-Hallpike maneuver or HINTS examination 1
• Missing stroke in patients with isolated dizziness (occurs in approximately 4% of cases) 1
• Failing to consider medication side effects as a cause of dizziness, particularly in elderly patients on multiple medications 2, 3

Algorithm for Laboratory Testing in Dizziness

1. Determine the type of dizziness based on timing and triggers 1
2. For vertigo: Focus on vestibular examination (nystagmus, Dix-Hallpike, HINTS) rather than laboratory testing 1, 6
3. For presyncope: Check orthostatic vitals, CBC, electrolytes, glucose, and consider cardiac evaluation 3, 5
4. For disequilibrium: Consider glucose testing (for diabetic neuropathy), vitamin B12 levels (for peripheral neuropathy) 2, 8
5. For lightheadedness: Consider CBC, thyroid function, and metabolic panel 2, 3
6. Order neuroimaging only when neurological deficits are present or HINTS examination suggests central cause 4, 7