What laboratory tests are recommended when evaluating depression?

Laboratory Tests Recommended for Depression Evaluation

When evaluating depression, routine laboratory testing should include a complete blood count, comprehensive metabolic panel, thyroid function tests (TSH, free T4), vitamin B12, and folate levels to rule out medical conditions that may cause or exacerbate depressive symptoms. 1, 2

Core Laboratory Tests

• Complete Blood Count (CBC): Essential to evaluate for anemia, which can contribute to fatigue and reduced quality of life in depressed patients 2

• Thyroid Function Tests: TSH and free T4 are critical as hypothyroidism can present with depressive symptoms or coexist with depression 3

• Vitamin B12 and Folate: Deficiencies can contribute to depressive symptoms and should be evaluated, particularly in elderly patients 2, 4

• Comprehensive Metabolic Panel: To assess liver and kidney function, electrolyte balance, and glucose levels, as metabolic disorders can manifest with depressive symptoms 5

Additional Testing Based on Clinical Presentation

• Iron Studies: Should be considered when anemia is detected on CBC to determine the specific type and cause 2

• Vitamin D Level: Consider testing as suboptimal vitamin D status is frequently observed in patients with depression 4

• Inflammatory Markers: Consider hs-CRP in patients with suspected inflammatory component to their depression 5

• Glucose Regulation Tests: Depression has been associated with poor glycemic control and insulin sensitivity 5

Special Considerations

• Elderly Patients: Pay particular attention to thyroid function, B12, and folate levels, as deficiencies are more common in this population 1

• Patients with Chronic Medical Conditions: More comprehensive testing may be warranted as depression often coexists with chronic illness 2

• Medication Effects: Consider testing that may reveal medication side effects that mimic depressive symptoms 1

Important Caveats

• Laboratory testing should complement, not replace, validated depression screening tools such as PHQ-9, BDI, HAM-D, or CES-D 6

• The U.S. Preventive Services Task Force emphasizes that screening for depression is only effective when followed by accurate diagnosis, appropriate treatment, and careful follow-up 2

• A positive depression screen requires further diagnostic questioning to establish an appropriate diagnosis and treatment plan 7

• Cultural factors, cognitive status, and age should be considered when interpreting both laboratory results and depression screening results 2

Clinical Approach Algorithm

1. Initial Evaluation: Perform validated depression screening (PHQ-9, BDI) 6
2. Basic Laboratory Panel: CBC, comprehensive metabolic panel, TSH, free T4, vitamin B12, folate 2, 3
3. Additional Testing: Based on clinical presentation, consider vitamin D, inflammatory markers, additional endocrine testing 5, 4
4. Interpretation: Integrate laboratory findings with clinical presentation to distinguish between primary depression and medical conditions presenting with depressive symptoms 1
5. Follow-up: Establish appropriate intervals to monitor both depression and any identified medical conditions 2