What laboratory tests should be ordered for a patient with chronic depression?

Laboratory Tests for Chronic Depression

For patients with chronic depression, a comprehensive laboratory workup should include thyroid-stimulating hormone (TSH), complete blood count (CBC), basic metabolic panel, liver function tests, and vitamin B12 levels to rule out medical conditions that can mimic or exacerbate depression. 1

Core Laboratory Tests

Essential Tests

• Thyroid Function Tests

  • TSH, free T4, and free T3
  • Rationale: Thyroid dysfunction has a well-established relationship with mood disorders 1
  • Even subclinical thyroid abnormalities can impact depression 1

• Complete Blood Count (CBC)

  • Screens for anemia, infection, or other hematologic abnormalities
  • Recommended by the American College of Physicians for depression evaluation 1

• Basic Metabolic Panel

  • Includes electrolytes, blood urea nitrogen (BUN), creatinine, and glucose
  • Helps rule out metabolic disturbances that can present with depressive symptoms 1

• Liver Function Tests

  • AST, ALT, and bilirubin
  • Liver dysfunction can contribute to depressive symptoms 1

• Vitamin B12 Level

  • B12 deficiency can present with or exacerbate depressive symptoms 1, 2

Additional Considerations

• Selenium and Vitamin D Levels

  • Both have been found to be decreased in depressed patients 2
  • Deficiencies may contribute to depressive symptoms

• Magnesium Level

  • Deficiency has been associated with depression 2
  • Shows inverse correlation with tryptophan in depressed patients

Special Populations

• Older Adults

  • More comprehensive testing may be needed due to higher prevalence of medical comorbidities
  • The Geriatric Depression Scale is an appropriate screening tool 3
  • American Geriatrics Society recommends thorough laboratory evaluation 1

• Monitoring During Treatment

  • Laboratory values may change during treatment
  • Periodic monitoring of thyroid function is recommended by the American Thyroid Association 1

Clinical Approach

1. Initial Screening: Use validated tools like PHQ-9 to confirm depression 3
2. Laboratory Evaluation: Order the core tests listed above
3. Evaluate Results: Look for abnormalities that could be causing or exacerbating depression
4. Treat Underlying Conditions: Address any identified medical issues
5. Monitor: Repeat testing periodically, especially thyroid function

Common Pitfalls

• Overlooking Medical Causes: Many medical conditions can mimic depression symptoms 4, 1
• Neglecting Comorbid Conditions: Screen for anxiety, substance use disorders, and other psychiatric conditions 1
• Missing Subclinical Thyroid Dysfunction: Even "normal" values at the extremes of range may be significant 1
• Inadequate Follow-up: Ensure systems are in place for diagnosis, treatment, and follow-up 4

Following this structured approach to laboratory testing in chronic depression will help identify potential medical contributors to depressive symptoms and guide appropriate treatment decisions.