What initial lab tests are recommended for a patient presenting with dizziness?

From the Guidelines

Initial laboratory tests for a patient presenting with dizziness should include a complete blood count (CBC), basic metabolic panel (BMP), thyroid function tests (TSH, free T4), and blood glucose measurement. The CBC helps identify anemia or infection that could contribute to dizziness 1. The BMP assesses electrolyte imbalances, particularly sodium, potassium, and calcium abnormalities, which can affect neurological function and cause dizziness. Thyroid function tests are important because both hypothyroidism and hyperthyroidism can manifest with dizziness as a symptom. Blood glucose measurement is crucial to rule out hypoglycemia or hyperglycemia, both of which can cause lightheadedness and dizziness.

In selected cases, additional tests may be warranted based on clinical suspicion, such as cardiac enzymes if cardiac causes are suspected, hemoglobin A1c in diabetic patients, or vitamin B12 and folate levels if nutritional deficiencies are considered 1. These laboratory tests complement the clinical evaluation, which should include a thorough history, physical examination, and possibly specialized tests like orthostatic vital signs or neurological examination to determine the specific cause of dizziness. The HINTS examination, which includes the head impulse, nystagmus, test of skew, can be useful in distinguishing between peripheral and central causes of vertigo, especially when performed by specially trained practitioners 1.

Some key points to consider when evaluating a patient with dizziness include:

• The presence of associated neurologic symptoms, which can increase the likelihood of a central cause such as stroke 1
• The use of bedside tests like the HINTS examination to distinguish between peripheral and central causes of vertigo 1
• The importance of clinical triage in determining the need for imaging evaluation of the central nervous system 1
• The low diagnostic yield of CT and MRI in patients with isolated dizziness without vertigo, ataxia, or other neurologic deficits 1

Overall, a thorough clinical evaluation, including a detailed history, physical examination, and selected laboratory tests, is essential in determining the cause of dizziness and guiding further management.

From the Research

Initial Lab Tests for Dizziness

The following lab tests are recommended for a patient presenting with dizziness:

• Complete Blood Cell Count (CBC) to rule out anemia, thrombocytopenia, leukopenia, polycythemia, thrombocytosis, and leukocytosis 2
• Blood glucose test to check for hypo or hyperglycemia, as impaired glucose metabolism is a common cause of dizziness 3, 4
• Four-hour glucose-insulin curve test to study glucose and insulin metabolism disorders, which are prevalent in patients with peripheral vestibular disorders 4
• Electrolyte panel to check for any electrolyte imbalances that may be contributing to dizziness

Rationale for Lab Tests

The lab tests are recommended based on the following rationales:

• Dizziness can be a symptom of various underlying conditions, including metabolic disorders, anemia, and electrolyte imbalances 3, 2, 4
• Impaired glucose metabolism is a common cause of dizziness, and blood glucose tests can help diagnose hypo or hyperglycemia 3, 4
• The four-hour glucose-insulin curve test can help identify glucose and insulin metabolism disorders, which are prevalent in patients with peripheral vestibular disorders 4
• A complete blood cell count (CBC) can help rule out anemia, thrombocytopenia, leukopenia, polycythemia, thrombocytosis, and leukocytosis, which can cause dizziness 2

Special Considerations

Special considerations should be taken into account when interpreting lab results, such as:

• Hypoglycemia can be associated with elevated troponin levels, which may indicate myocardial damage 5
• The diagnosis of hypoglycemia requires a combination of clinical criteria, including symptoms, timing of symptoms, and low blood sugar levels 6