What laboratory tests are recommended for a patient presenting with depression, considering their medical history and potential underlying conditions?

Laboratory Testing for Depression

Obtain thyroid function studies (TSH), complete blood count, liver function tests, and metabolic panels as baseline laboratory testing before initiating treatment for depression. 1

Core Laboratory Panel

The following tests should be obtained for all patients presenting with depression:

• Thyroid-stimulating hormone (TSH) to rule out thyroid-induced depressive symptoms, though overt thyroid disease is rare (0.4% hyperthyroidism, 0% overt hypothyroidism in depressed patients). 1
• Complete blood count (CBC) to establish baseline values and identify potential contributing medical conditions. 1
• Liver function tests to establish baseline before antidepressant initiation and monitor for treatment-related adverse effects. 1
• Metabolic panel to screen for electrolyte abnormalities and establish baseline kidney function. 1

These tests serve two critical purposes: identifying medical conditions that may contribute to depressive symptoms and establishing baseline values for monitoring treatment-related adverse effects. 1

When to Expand Laboratory Testing

Additional testing should be guided by clinical presentation, risk factors, and suspected comorbid conditions rather than routine extensive screening. 1

The evidence strongly supports selective rather than routine extensive laboratory testing:

• Multiple studies demonstrate that routine laboratory screening is unnecessary and that testing should be guided by clinical evaluation. 2
• False-positive laboratory results occur 8 times more frequently than true positives (1.8%) in patients undergoing routine testing. 2
• Most abnormal laboratory values obtained through routine screening are clinically insignificant. 2

High-Risk Populations Requiring More Extensive Evaluation

Expand laboratory testing for patients with:

• First psychiatric presentation or new psychiatric symptoms (these patients particularly need careful medical evaluation). 2
• Elderly patients (consider ECG, chest radiograph, blood urea nitrogen, and vitamin B12 in psychogeriatric populations). 2
• Substance abuse history (requires targeted screening based on substances used). 2
• Patients without prior psychiatric history (higher likelihood of medical etiology). 2
• Preexisting or new medical complaints (requires evaluation of specific organ systems). 2
• Lower socioeconomic status (identified as additional risk factor). 2

Critical Safety Monitoring During Treatment

• Repeat laboratory tests before each medication adjustment to monitor for treatment-related complications. 1
• Monitor specifically for hyponatremia (especially in elderly patients), liver function changes, and metabolic effects. 1

Common Pitfalls to Avoid

Do not order extensive routine laboratory batteries without clinical indication. The preponderance of evidence concludes that selective testing based on clinical evaluation is the correct strategy, as routine extensive testing yields mostly false positives and clinically insignificant results. 2

Do not skip baseline testing before initiating antidepressants. While extensive screening is unnecessary, the core panel (TSH, CBC, liver function, metabolic panel) is essential for safe prescribing and monitoring. 1

Do not forget that laboratory testing alone cannot diagnose depression. Depression diagnosis requires clinical interview using DSM-5 criteria—laboratory tests only help rule out medical mimics and establish treatment baselines. 1, 3