What is the initial lab workup for a patient presenting with dizziness?

Initial Laboratory Workup for Dizziness

The initial laboratory workup for a patient presenting with dizziness should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, blood glucose, liver function tests, and thyroid-stimulating hormone.

Diagnostic Approach to Dizziness

Initial Assessment

• Categorize dizziness based on timing and triggers rather than symptom quality 1
• Perform targeted history focusing on:
  • Onset and duration of symptoms
  • Associated symptoms (nausea, vomiting, headache)
  • Triggers (positional changes, specific movements)
  • Risk factors for stroke or cardiac disease

Physical Examination

• Orthostatic blood pressure measurements 1
• Neurological assessment including cranial nerves
• Dix-Hallpike maneuver for suspected BPPV
• HINTS examination (Head-Impulse, Nystagmus, Test of Skew) for acute vestibular syndrome 1
• 12-lead ECG to rule out cardiac causes

Laboratory Investigations

Essential Laboratory Tests

• Complete blood count - to evaluate for anemia or infection 1, 2
• Basic metabolic panel - to assess electrolyte abnormalities 1
• Serum electrolytes including calcium and magnesium - electrolyte imbalances can cause dizziness 1
• Blood urea nitrogen and serum creatinine - to evaluate renal function 1
• Blood glucose - routine testing is supported in all dizzy patients 1, 2
• Liver function tests - to rule out metabolic causes 1
• Thyroid-stimulating hormone - thyroid dysfunction can present with dizziness 1
• Urinalysis - to screen for infection or dehydration 1

Additional Testing Based on Clinical Presentation

For patients with high-risk features (age ≥65 years, ataxia, focal neurological symptoms, history of stroke or diabetes):

• Consider brain imaging (MRI preferred over CT) 1, 3
• Cardiac monitoring if age ≥45 or suspected cardiac cause 2

Red Flags Requiring Urgent Evaluation

• Sudden severe headache with dizziness
• New neurological symptoms or deficits
• Inability to walk or stand
• Persistent vomiting with dizziness
• Altered mental status 1

Common Pitfalls to Avoid

1. Overreliance on symptom quality: Focus on timing and triggers rather than how patients describe their dizziness 1, 4

2. Unnecessary testing: Avoid ordering extensive tests for all patients. The basic laboratory panel above is sufficient for initial evaluation 2, 5

3. Missing peripheral vestibular disorders: These are common (43% of dizziness cases) and often manageable in outpatient settings 2

4. Overlooking medication causes: Always review current medications as potential causes of dizziness 1

5. Failure to identify high-risk patients: Age ≥65 years, ataxia, focal neurological symptoms, history of stroke, and diabetes are predictors of central neurological causes 3

By following this systematic approach to laboratory workup for dizziness, clinicians can efficiently identify the underlying cause while minimizing unnecessary testing and avoiding missed diagnoses of potentially serious conditions.