Laboratory Testing for Dizziness
In most patients presenting with dizziness, routine laboratory testing is not indicated and should be guided by specific clinical findings from the history and physical examination rather than ordered as a blanket panel. 1, 2
Selective Testing Based on Clinical Presentation
High-Yield Laboratory Tests
Serum glucose is the single most frequently abnormal laboratory test in dizziness evaluations and should be checked in patients with diabetes, those taking hypoglycemic agents, or those with prolonged fasting. 1, 3
- In prospective studies of patients with new-onset seizures and dizziness, hypoglycemia was the most common unsuspected laboratory abnormality, occurring in 1-4 cases per 100-250 patients 3
- Hyperglycemia was also identified but typically predicted by clinical history 3
Patients Requiring Targeted Laboratory Evaluation
Order complete blood count, electrolytes, renal function, and glucose in patients with altered mental status, fever, or new focal neurologic deficits. 1, 3
- Hyponatremia is the second most common metabolic abnormality, though usually suspected based on history (psychogenic water ingestion, diuretic use) 3
- In one prospective study of 98 patients, only 1 case of unsuspected hyponatremia was found 3
For patients with suspected cardiac etiology of dizziness, obtain complete blood count, urinalysis, electrolytes, blood urea nitrogen, creatinine, fasting glucose, lipid profile, liver function tests, and thyroid-stimulating hormone. 1
- TSH should be considered specifically in patients with cardiac symptoms or known heart failure 1
Pregnancy testing is essential in women of childbearing age, as it affects diagnostic testing decisions, disposition, and potential medication choices. 1, 3
- In one study of 59 patients with new-onset seizures during pregnancy, identification of pregnancy status was critical for management 3
Tests NOT Supported by Evidence
Routine calcium, magnesium, and phosphate testing is not indicated in otherwise healthy patients with dizziness. 1, 3
- In prospective studies, hypocalcemia was found only in patients with known cancer or renal failure 3
- Hypomagnesemia occurred only in alcoholic patients 3
- No prospective data support routine testing of these electrolytes in healthy individuals 3
Clinical Approach Algorithm
Step 1: Risk Stratification
- Low-risk patients (isolated dizziness, normal vital signs, no neurologic deficits): No routine laboratory testing required 1, 2
- High-risk patients (altered mental status, fever, focal deficits, cardiac symptoms): Targeted laboratory evaluation indicated 1, 3
Step 2: Specific Clinical Scenarios
- Suspected benign paroxysmal positional vertigo: No laboratory testing needed 2, 4
- Suspected Menière disease: No routine laboratory testing indicated 2, 5
- Suspected vestibular neuritis: No laboratory testing required 5
- Suspected transient ischemic attack: Full blood count, electrolytes, renal function, cholesterol, glucose, and ECG 3
Step 3: Medication Review
- Check glucose if patient takes hypoglycemic agents 1
- Review medications that may cause presyncope or orthostatic hypotension 2
- No specific laboratory panels required for medication-induced dizziness 4
Common Pitfalls to Avoid
Avoid ordering "routine panels" without clinical justification, as this approach is not cost-effective and rarely changes management. 1
- The positivity rate of laboratory testing in isolated dizziness is extremely low (approximately 2-4% for any abnormality) 3
- History and physical examination predict the majority of patients who will have laboratory abnormalities 3
Do not order extensive metabolic panels based on patient anxiety rather than clinical indication, as this leads to false positives and unnecessary follow-up. 1
Recognize that imaging studies (CT, MRI) have higher diagnostic yield than laboratory testing in dizziness, but even these should be clinically guided rather than routine. 3, 2