What are the diagnostic tests and treatment options for depression, including the role of blood tests such as thyroid function tests and complete blood counts?

Diagnostic Tests and Treatment Options for Depression

Blood tests are not routinely recommended for all patients with depression but should be selectively ordered based on clinical history and physical examination findings to rule out medical conditions that may cause or exacerbate depressive symptoms.

Diagnostic Approach for Depression

Screening and Diagnosis

• Depression screening can be effectively done using simple tools:
  • Two simple questions about mood and anhedonia ("Over the past 2 weeks, have you felt down, depressed, or hopeless?" and "Over the past 2 weeks, have you felt little interest or pleasure in doing things?") are as effective as longer instruments 1
  • Formal screening tools with good sensitivity (80-90%) include the Zung Self-Depression Scale, Beck Depression Inventory, General Health Questionnaire, and Center for Epidemiologic Study Depression Scale 1
  • Positive screening should trigger a full diagnostic interview using standard DSM criteria 1

Laboratory Testing

Laboratory testing should be selective rather than routine, based on clinical presentation:

1. Thyroid Function Tests:

   • Recommended for patients with depression, particularly those with atypical presentations or treatment resistance 1
   • Approximately 20% of depressed patients may have detectable antithyroid antibodies (compared to 5-10% in general population) 2
   • Thyroid dysfunction can present with mood, anxiety, psychotic, and cognitive symptoms 3

2. Complete Blood Count:

   • Should be considered selectively based on clinical presentation 1
   • Not recommended as routine screening for all patients with depression 1

3. Other Selective Tests (based on clinical indication):

   • Basic metabolic panel/electrolytes
   • Liver function tests
   • Urinalysis
   • Toxicology screen (when substance use is suspected)
   • Vitamin B12 levels (especially in older adults)

Neuroimaging and Additional Testing

• Not routinely indicated for uncomplicated depression
• Consider in cases with:
  • New-onset psychosis
  • Neurological symptoms
  • History of head trauma
  • First episode in older adults (>65)
  • Treatment-resistant depression

Medical Conditions That Can Mimic Depression

Several medical conditions can present with depressive symptoms and should be ruled out:

1. Endocrine Disorders:

   • Hypothyroidism and hyperthyroidism
   • Cushing's disease
   • Addison's disease
   • Hyperparathyroidism

2. Neurological Conditions:

   • Stroke/TIA
   • CNS tumors
   • Parkinson's disease
   • Multiple sclerosis
   • Dementia 1

3. Metabolic Disorders:

   • Vitamin deficiencies (B12, folate)
   • Electrolyte abnormalities
   • Hypoglycemia

4. Medication-Induced Depression:

   • Beta-blockers
   • Corticosteroids
   • Some antihypertensives
   • Interferon
   • Hormonal contraceptives

Treatment Options for Depression

Pharmacotherapy

• Antidepressants are effective for treating depression in adults 1
• Consider age-specific concerns:
  • For patients 18-29 years: Consider psychotherapy or non-SSRI medications due to increased risk of suicidal behavior with SSRIs 1
  • For patients ≥65 years: Consider psychotherapy or non-SSRI medications due to increased risk of upper GI bleeding with SSRIs 1

Psychotherapy

• Effective treatment options include:
  • Cognitive-behavioral therapy
  • Interpersonal therapy
  • Brief psychosocial counseling
  • These can be used alone or in combination with medication 1

Combined Approach

• Combination of medication and psychotherapy may be more effective than either treatment alone, particularly for moderate to severe depression

Special Considerations

Treatment Resistance

• For patients not responding to initial treatment:
  • Evaluate thyroid function if not already done 4
  • Consider TRH stimulation test which may have prognostic value 5
  • Consider switching antidepressant class or augmentation strategies

Medical Comorbidities

• Depression often coexists with chronic medical conditions
• Treatment should address both the depression and underlying medical conditions
• Tricyclic antidepressants may be effective in treating depressive symptoms associated with medical illness 6

Monitoring

• Regular follow-up to assess response to treatment
• Monitor for side effects of medications
• Reassess diagnosis if poor response to treatment

By following this evidence-based approach to diagnosing and treating depression, clinicians can effectively identify and manage depression while ruling out medical conditions that may present with similar symptoms.