How is depression diagnosed?

How to Diagnose Depression

Depression is diagnosed through a two-step process: initial screening using validated questionnaires (PHQ-2 or PHQ-9), followed by confirmation with DSM criteria through clinical interview when screening is positive.

Screening Approach

First-Line Screening Tools

Start with the PHQ-2, which asks two simple questions 1:

• "Over the past 2 weeks, have you felt down, depressed, or hopeless?"
• "Over the past 2 weeks, have you felt little interest or pleasure in doing things?"

The PHQ-2 has sensitivity comparable to longer instruments but lower specificity (78-92% vs 91-94% for PHQ-9) 2. If the PHQ-2 is positive, immediately administer the PHQ-9 or conduct a full clinical interview 1, 2.

Alternative Screening Instruments

Other validated tools include 1:

• Beck Depression Inventory (BDI): 21 items; scores ≥20 suggest clinical depression
• Center for Epidemiological Studies Depression Scale (CES-D): 20 items; scores ≥16 suggest moderate-to-severe depression; relatively unaffected by physical symptoms
• Hamilton Depression Rating Scale (HAM-D): Clinician-administered; 7-17 = mild, 18-24 = moderate, ≥25 = severe depression
• Hospital Anxiety and Depression Scale (HADS): 14 items; score ≥8 indicates probable disorder; excludes physical symptoms

Special Populations

• Older adults: Use Geriatric Depression Scale (GDS); score ≥19 (30-item) or ≥5 (15-item short form) suggests depression 1, 2
• Postpartum women: Screen at least once during perinatal period with PHQ-2, PHQ-9, or Edinburgh Postnatal Depression Scale 2
• Children/adolescents 12-18 years: Screen using age-appropriate tools; note that irritable mood can substitute for depressed mood 3, 4

Diagnostic Confirmation

DSM Criteria for Major Depressive Disorder

All positive screens must be confirmed with full diagnostic interview using DSM criteria 1, 5. Diagnosis requires:

Core symptoms (at least one must be present) 6, 5:

1. Depressed mood most of the day, nearly every day (or irritable mood in children/adolescents)
2. Markedly diminished interest or pleasure in activities (anhedonia)

Additional symptoms (total of 5+ symptoms including core symptoms) 3, 6, 5: 3. Significant weight change (>5% body weight in a month) or appetite disturbance 4. Insomnia or hypersomnia nearly every day 5. Psychomotor agitation or retardation (observable by others) 6. Fatigue or loss of energy 7. Feelings of worthlessness or inappropriate guilt 8. Diminished ability to think, concentrate, or indecisiveness 9. Recurrent thoughts of death or suicidal ideation

Duration and impact 6, 5:

• Symptoms must persist for at least 2 weeks
• Must cause clinically significant distress or functional impairment in social, occupational, or other important areas

Essential Exclusions

Before confirming depression diagnosis, rule out 3, 6:

• Medical causes: Hypothyroidism, medication side effects (e.g., interferon), substance use
• Mixed episodes: Fluctuating mood meeting criteria for both manic and depressive episodes
• Bereavement: Unless symptoms persist >2 months, include marked functional impairment, morbid preoccupation with worthlessness, suicidal ideation, psychotic symptoms, or psychomotor retardation

Clinical Pearls

Red Flags Requiring Immediate Action

Any patient identified as at risk of harm to self or others requires immediate referral for emergency psychiatric evaluation 1. Facilitate safe environment and one-to-one observation.

Efficient Screening Strategy

A practical shortcut: If patients have neither general fatigue, nor sleep disturbance, nor appetite loss, depression is highly unlikely 7. Conversely, depression prevalence increases dramatically with number of physical symptoms: 2% with 0-1 symptoms, 42% with 4-5 symptoms, 68% with >9 symptoms 7.

When to Refer

Recognition of depression should trigger referral to a mental health provider skilled in treating this population 3. Refer immediately for 1:

• Severe depression or agitation
• Psychosis or confusion (delirium)
• Risk of self-harm or harm to others
• Moderate-to-severe symptomatology detected on screening

Common Pitfalls

• Don't rely on screening scores alone: Positive screens require diagnostic confirmation with DSM criteria 1, 2
• Don't miss medical causes: Always assess for substance-induced or medically-induced depression (e.g., medications, hypothyroidism) 3, 1
• Don't overlook comorbidities: Assess for anxiety, panic, substance abuse, and chronic medical conditions 1, 8
• Don't forget functional assessment: Document impairment in work, relationships, and daily activities 6, 5