What is the appropriate initial laboratory workup for a teenager presenting with depression?

Initial Laboratory Workup for Adolescents with Depression

The appropriate initial laboratory workup for a teenager presenting with depression should include a complete blood count (CBC), comprehensive metabolic panel (CMP), thyroid function tests (TSH, free T4), and vitamin D levels to rule out medical conditions that may mimic or exacerbate depressive symptoms. 1

Rationale for Laboratory Testing

Depression in adolescents requires careful evaluation to distinguish between primary psychiatric disorders and medical conditions that may present with depressive symptoms. Laboratory testing serves as an essential component of this assessment process.

Core Laboratory Tests

• Complete Blood Count (CBC)

  • Screens for anemia, which can cause fatigue and depressive symptoms
  • Evaluates for signs of infection or inflammation

• Comprehensive Metabolic Panel (CMP)

  • Assesses electrolyte imbalances that may affect mood
  • Evaluates kidney and liver function
  • Screens for glucose abnormalities

• Thyroid Function Tests

  • TSH and free T4 to detect hypothyroidism or hyperthyroidism
  • Thyroid dysfunction can present with mood disturbances resembling depression

• Vitamin D Level

  • Low vitamin D has been associated with depressive symptoms
  • Particularly important in adolescents with limited sun exposure

Additional Testing Based on Clinical Presentation

Beyond the core laboratory tests, additional testing should be considered based on specific clinical presentations:

• Substance Use Screening

  • Urine toxicology if substance use is suspected
  • Substance use is a common comorbidity and can exacerbate depressive symptoms 1

• Endocrine Testing

  • Consider testing for cortisol levels if Cushing's syndrome is suspected
  • Evaluate sex hormones if menstrual irregularities are present

• Iron Studies

  • Ferritin, iron, and total iron-binding capacity if anemia is suspected
  • Iron deficiency can contribute to fatigue and mood symptoms

Clinical Context for Laboratory Evaluation

The American Academy of Pediatrics recommends comprehensive assessment that includes both psychiatric evaluation and medical screening 1. This approach is essential because:

1. Medical conditions can mimic or exacerbate depressive symptoms
2. Certain medical conditions require specific treatment before or alongside depression treatment
3. Baseline laboratory values are important before initiating pharmacotherapy

Important Considerations

• Laboratory testing should complement, not replace, thorough clinical assessment including direct interviews with the adolescent and family 1, 2
• Normal laboratory findings do not rule out depression, as most adolescents with depression have normal laboratory values
• Laboratory results should be interpreted in the context of the clinical presentation
• Follow-up testing may be necessary based on initial findings or treatment response

When to Consider Referral

Consider referral to a mental health specialist when:

• Laboratory findings suggest medical causes of depressive symptoms
• Depression is severe, includes psychotic features, or involves suicidal ideation
• There is poor response to initial treatment
• Comorbid conditions complicate diagnosis or treatment

Remember that laboratory testing is just one component of a comprehensive assessment that should include standardized depression screening tools, clinical interviews, and evaluation of functional impairment across multiple domains 1, 2.