What labs should be ordered for a patient presenting with fatigue and dizziness?

Laboratory Evaluation for Fatigue and Dizziness

For patients presenting with fatigue and dizziness, a comprehensive laboratory evaluation should include complete blood count, comprehensive metabolic panel, thyroid function tests, iron studies, vitamin D level, and inflammatory markers as the initial diagnostic approach. 1

Initial Laboratory Workup

Essential First-Line Tests

• Complete Blood Count (CBC) with differential

  • Evaluates for anemia, infection, and other hematologic abnormalities
  • Particularly important as anemia is a common cause of both fatigue and dizziness

• Comprehensive Metabolic Panel (CMP)

  • Includes:
    • Electrolytes (sodium, potassium, chloride, bicarbonate)
    • Glucose (for diabetes screening)
    • Kidney function (BUN, creatinine)
    • Liver function tests

• Thyroid Function Tests

  • TSH as primary screening test
  • Free T4 if TSH is abnormal
  • Thyroid dysfunction is a common cause of fatigue 2

• Iron Studies

  • Serum iron
  • Ferritin
  • Total iron binding capacity (TIBC)
  • Transferrin saturation
  • Important as iron deficiency can cause fatigue even before anemia develops 1

• Vitamin D Level (25-hydroxyvitamin D)

  • Low levels are associated with fatigue and muscle weakness 1

• Inflammatory Markers

  • ESR (erythrocyte sedimentation rate)
  • CRP (C-reactive protein)
  • Helps identify inflammatory conditions that may cause fatigue

Second-Line Tests Based on Clinical Suspicion

• Fasting Blood Glucose/HbA1c

  • For diabetes screening, especially if polyuria or polydipsia are present

• Cortisol Level

  • Morning cortisol to screen for adrenal insufficiency
  • Consider if orthostatic hypotension is present with fatigue

• Sex Hormone Levels

  • Particularly in patients with other symptoms of hypogonadism

• BNP or NT-proBNP

  • If heart failure is suspected as a cause of fatigue and dizziness

• Autoimmune Markers

  • Consider if rheumatologic disease is suspected based on other symptoms

• Urinalysis

  • To screen for infection, kidney disease, and diabetes

Special Considerations

For Dizziness Evaluation

• Consider vestibular testing if laboratory workup is normal and dizziness persists
• Evaluate for BPPV (Benign Paroxysmal Positional Vertigo) as it commonly presents with both dizziness and fatigue 3

For Persistent Symptoms Despite Normal Initial Labs

• Consider expanded testing when symptoms persist despite normal initial workup
• Evaluate for psychiatric causes including anxiety and depression, which can manifest as both fatigue and dizziness 4

Nutritional Considerations

• Evaluate for poor nutrition or excessive alcohol intake, which can lead to electrolyte disturbances presenting as fatigue and dizziness 5
• Consider magnesium levels in patients with malabsorption conditions

Common Pitfalls to Avoid

1. Overlooking thyroid dysfunction: Even subclinical thyroid disorders can cause significant fatigue 6

2. Missing electrolyte abnormalities: Hyponatremia and hypokalemia can cause both fatigue and dizziness but may be overlooked 5

3. Ignoring medication side effects: Many medications can cause fatigue and dizziness as side effects

4. Failing to consider psychiatric causes: Anxiety and depression commonly present with somatic symptoms including fatigue and dizziness 4

5. Not evaluating for chronic conditions: Conditions like inflammatory bowel disease can cause fatigue even during remission 2

By following this systematic approach to laboratory evaluation, clinicians can efficiently identify the underlying causes of fatigue and dizziness, leading to appropriate treatment and improved patient outcomes.