Initial Laboratory Testing and Treatment for Depression

Laboratory Testing Recommendations

Thyroid function studies (TSH) should be obtained as part of the baseline assessment to rule out thyroid-induced depressive symptoms, though overt thyroid disease is rare among depressed patients (0.4% hyperthyroidism, 0% overt hypothyroidism in one study) 1
Complete blood counts, liver function tests, and metabolic panels should be obtained at baseline before initiating treatment, particularly for patients who will receive antidepressant medications 1
These tests help identify medical conditions that may contribute to depressive symptoms and establish baseline values for monitoring treatment-related adverse effects 1
Additional testing should be guided by clinical presentation, risk factors, and suspected comorbid conditions (substance use, medical illness) 2

Use the PHQ-9 as the primary screening tool, which has sensitivity of 89.5% and specificity of 77.5% at a cutoff score of ≥11 for detecting major depressive disorder 3
A two-step approach can be used: start with PHQ-2 (first two questions about depressed mood and anhedonia); if positive (score ≥2), complete the full PHQ-9 4, 3
The recommended cutoff score is ≥8 based on studies in specific populations, though the traditional cutoff is ≥10 5, 3
All positive screens require direct clinical interview using DSM-5 criteria to confirm diagnosis—screening alone does not establish a diagnosis 4, 2
Assess for suicidal ideation (PHQ-9 item 9), bipolar disorder risk, psychotic symptoms, substance use, and comorbid anxiety disorders 2
Evaluate functional impairment across multiple domains (work, relationships, self-care) 2
Obtain collateral information from family members when possible 2

Provide education about depression and normal stress responses for patients with mild symptoms (PHQ-9: 1-7) 3
Ensure adequate coping skills and access to resources for patients with mild symptoms (PHQ-9: 1-7) 3
Consider reassessment at future visits, particularly for patients with risk factors and mild symptoms (PHQ-9: 1-7) 3
Evaluate for pertinent history and specific risk factors (family history, previous episodes, trauma, psychosocial stressors) for patients with moderate symptoms (PHQ-9: 8-14) 2, 3
Consider referral to psychology or psychiatry for diagnostic evaluation and treatment initiation for patients with moderate symptoms (PHQ-9: 8-14) 3
Make immediate referral to psychology and/or psychiatry for diagnosis and treatment for patients with moderate-to-severe/severe symptoms (PHQ-9: 15-27) 3
Assess for risk of harm to self or others immediately—any endorsement of specific plans or intent requires emergency intervention for patients with moderate-to-severe/severe symptoms (PHQ-9: 15-27) 5, 3

Psychotherapy is as effective as medication for major depression but more time-intensive 6, 7
Effective psychotherapies include cognitive therapy, behavioral activation, problem-solving therapy, interpersonal therapy, brief psychodynamic therapy, and mindfulness-based psychotherapy, all with medium-to-large effect sizes (SMD 0.50-0.73) 6, 7

Obtain laboratory tests before each medication adjustment and monitor for hyponatremia (especially in elderly), liver function changes, and metabolic effects 1

Do not rely on screening scores alone for diagnosis—false-positive rates are 60-76% in primary care settings with 5-10% depression prevalence 6, 7
Do not overlook comorbid conditions (anxiety, substance use, PTSD) that affect treatment selection and outcomes 6, 7

The American College of Emergency Physicians supports selective rather than routine extensive laboratory testing for patients with depression, as routine laboratory screening is unnecessary and yields mostly false positives and clinically insignificant results 8
False-positive laboratory results occur 8 times more frequently than true positives (1.8%) in patients undergoing routine testing, highlighting the need for targeted testing 8
Most abnormal laboratory values obtained through routine screening are clinically insignificant, and testing should be guided by clinical evaluation 8

Patients with first psychiatric presentation or new psychiatric symptoms require careful medical evaluation and expanded laboratory testing 8
Elderly patients may require additional testing, including ECG, chest radiograph, blood urea nitrogen, and vitamin B12, due to increased risk of medical comorbidities 8
Patients with a history of substance abuse require targeted screening based on substances used, to identify potential contributing medical conditions 8
Patients without prior psychiatric history are at higher likelihood of medical etiology and may require more extensive evaluation 8
Patients with preexisting or new medical complaints require evaluation of specific organ systems to rule out underlying medical conditions 8
Lower socioeconomic status is identified as an additional risk factor for patients with depression, requiring careful consideration in testing and treatment 8

The American College of Emergency Physicians recommends against ordering extensive routine laboratory batteries without clinical indication, as this approach yields mostly false positives and clinically insignificant results 8