How do I diagnose major depressive disorder (MDD) while still in the assessment phase?

Diagnosing Major Depressive Disorder During Assessment

Use DSM-5 diagnostic criteria requiring 5 or more specific symptoms present for at least 2 weeks, with at least one being depressed mood or anhedonia, combined with a validated screening tool like the PHQ-9 to guide your clinical interview. 1

Core Diagnostic Criteria

The diagnosis of MDD requires meeting specific threshold criteria during your assessment 1:

• At least 5 of 9 symptoms must be present within the same 2-week period and represent a change from previous functioning 1
• At least one symptom must be either depressed mood (or irritable mood in adolescents) OR markedly diminished interest/pleasure in activities 1

The 9 DSM Symptom Criteria to Assess:

1. Depressed mood most of the day, nearly every day (can be irritable mood in children/adolescents) 1
2. Markedly diminished interest or pleasure in all or nearly all activities most of the day 1
3. Significant weight loss/gain (>5% body weight in a month) or appetite changes 1
4. Insomnia or hypersomnia nearly every day 1
5. Psychomotor agitation or retardation nearly every day (observable by others) 1
6. Fatigue or loss of energy nearly every day 1
7. Feelings of worthlessness or inappropriate guilt nearly every day 1
8. Diminished ability to think, concentrate, or indecisiveness nearly every day 1
9. Recurrent thoughts of death, suicidal ideation, suicide attempt, or specific plan 1

Structured Assessment Approach

Step 1: Use Validated Screening Tools

Begin with the PHQ-9 (9-item self-report scale) as it directly assesses DSM-IV/DSM-5 MDD symptoms and functional impairment 1. A positive screen (typically score ≥10) triggers full diagnostic evaluation but does not establish diagnosis alone 1.

Alternative validated tools include 1:

• HAM-D (17-item): Clinician-administered; scores 7-17 suggest mild, 18-24 moderate, ≥25 severe depression 1
• BDI: Scores ≥20 suggest clinical depression 1
• CES-D: Scores ≥16 suggest moderate to severe symptoms; relatively unaffected by physical symptoms 1

Step 2: Conduct Direct Clinical Interview

Screening tools alone cannot diagnose MDD 1. You must conduct a direct interview with the patient (and family/caregivers when appropriate) to 1:

• Verify the presence and duration of each DSM symptom criterion
• Assess whether symptoms cause clinically significant distress or functional impairment 1
• Evaluate impairment across multiple domains: school/work, home, peer/social relationships 1
• Obtain collateral information from other sources (teachers, family) when available 1

Step 3: Apply Exclusion Criteria

Before finalizing the diagnosis, rule out 1:

• Medical causes: Symptoms not due to direct physiologic effects of substances (drugs, medications) or general medical conditions (e.g., hypothyroidism, unrelieved pain, delirium from infection/electrolyte imbalance) 1
• Bipolar disorder: Symptoms do not meet criteria for mixed episode; screen for history of manic/hypomanic episodes 1
• Bereavement: Symptoms not better accounted for by normal grief 1
• Other psychiatric disorders: Symptoms not better explained by other mental disorders 1
• Active severe substance use disorder: Should be excluded 1

Step 4: Assess Comorbidities and Risk

Evaluate for common comorbid conditions that affect diagnosis and treatment 1:

• Other psychiatric disorders (anxiety, panic, substance use) 1
• Assess suicide risk in all patients; immediately refer those at risk of harm to self/others for emergency evaluation 1

Common Pitfalls to Avoid

Do not diagnose based on screening score alone. The PHQ-9 has excellent sensitivity (92.2%) but poor specificity (54.3%), leading to overdiagnosis if used without clinical interview 2. A positive screen requires full diagnostic evaluation 1.

Do not overlook atypical presentations. Adolescents may present with irritability rather than depressed mood, and patients may report somatic complaints (fatigue, pain, insomnia) rather than mood symptoms 1. Probe systematically for all 9 criteria even when not volunteered 1.

Do not miss medical causes. Always treat underlying medical causes of depressive symptoms first (pain, fatigue, infection, electrolyte imbalance, hypothyroidism) before attributing symptoms to primary MDD 1.

Documentation During Assessment

Record 1:

• Specific symptoms present and their duration
• Functional impairment in each domain
• Exclusion criteria evaluated
• Comorbid conditions identified
• Suicide risk assessment
• Screening tool scores (if used)

This systematic approach ensures accurate diagnosis while you are still gathering information during the assessment phase.