What is the diagnostic approach for depression in adults, considering factors such as age, sex, and medical comorbidities?

How to Diagnose Depression in Adults

Begin screening with the 2-item Patient Health Questionnaire (PHQ-2) asking about depressed mood and anhedonia over the past 2 weeks, and if positive (score ≥2), proceed to the full PHQ-9 or clinical diagnostic interview using DSM criteria. 1, 2

Initial Screening Approach

Use the PHQ-2 as your first-line screening tool by asking these two questions about the past 2 weeks: "Have you felt down, depressed, or hopeless?" and "Have you felt little interest or pleasure in doing things?" 1

• If PHQ-2 score is 0-1: No further screening needed 1
• If PHQ-2 score is 2-3: Proceed to full PHQ-9 or structured diagnostic interview 1

The PHQ-2 has sensitivity comparable to the PHQ-9, though specificity is lower (78-92% versus 91-94%), making it an efficient initial screen 3

Comprehensive Assessment Tools

When screening is positive, use validated instruments to quantify severity and guide diagnosis:

For General Adult Population

• PHQ-9 (9 items): Assesses all DSM-IV major depressive disorder symptoms with scoring: 1-7 (minimal), 8-14 (moderate), 15-19 (moderately severe), 20-27 (severe) 1, 2
• Beck Depression Inventory (BDI, 21 items): Scores ≥20 suggest clinical depression; assesses behavioral, cognitive, and somatic components including suicidal ideation 1, 2
• Hamilton Rating Scale for Depression (HAM-D, 17 items): Clinician-administered scale with scores 7-17 (mild), 18-24 (moderate), ≥25 (severe depression) 1, 2
• Center for Epidemiological Studies-Depression Scale (CES-D, 20 items): Scores ≥16 suggest moderate to severe symptomatology; relatively unaffected by physical symptoms 1, 2

For Older Adults (≥65 years)

Use the Geriatric Depression Scale (GDS) as it is specifically designed for elderly patients and excludes somatic symptoms that may confuse diagnosis: 1

• GDS (30 items): Score ≥19 suggests depression requiring follow-up
• GDS-SF (15 items): Score ≥5 suggests depression requiring follow-up

For Patients with Medical Comorbidities

Use the Hospital Anxiety and Depression Scale (HADS, 14 items) as it excludes physical symptom items that could be attributable to medical illness rather than depression 1

• Score ≥8 on the depression subscale indicates probable depression based on ICD-9 criteria

Formal Diagnostic Confirmation

All positive screening tests must trigger a full diagnostic interview using DSM criteria to confirm the presence of major depressive disorder or dysthymia 1

DSM Diagnostic Criteria Requirements

To diagnose major depressive disorder, the patient must have: 4

• At least 5 of 9 symptoms present during the same 2-week period
• At least one symptom must be either depressed mood or anhedonia (loss of interest/pleasure)
• Symptoms must cause clinically significant functional impairment in work, relationships, self-care, or daily activities 5

The 9 symptoms include: 4

1. Depressed mood
2. Anhedonia (loss of interest or pleasure)
3. Significant weight/appetite change
4. Sleep disturbance (insomnia or hypersomnia)
5. Psychomotor agitation or retardation
6. Fatigue or loss of energy
7. Feelings of worthlessness or excessive guilt
8. Diminished concentration or indecisiveness
9. Recurrent thoughts of death or suicidal ideation

Critical Safety Assessment

Always assess for suicidal ideation, homicidal ideation, and self-harm thoughts regardless of screening score or symptom severity 5, 1

• If any risk of self-harm or harm to others is identified: Immediately refer for emergency psychiatric evaluation, facilitate a safe environment with one-to-one observation, and initiate harm-reduction interventions 1, 5
• Never omit the suicidal ideation question as doing so artificially lowers risk detection and misses critical safety information 5

Exclude Medical Causes First

Before attributing symptoms to primary depression, rule out medical causes and substance-induced symptoms: 1, 5

• Uncontrolled pain or fatigue
• Delirium from infection or electrolyte imbalance
• Thyroid disorders (hypothyroidism or hyperthyroidism)
• Medication side effects (corticosteroids, beta-blockers, benzodiazepines)
• Substance use or withdrawal

Special Population Considerations

Women

Women have twice the lifetime risk of depression compared to men (30% versus 17%) and should be screened at least once during the perinatal period using PHQ-2, PHQ-9, or Edinburgh Postnatal Depression Scale 3, 6

Patients with Chronic Medical Illness

Use screening tools that minimize somatic symptom overlap (HADS or CES-D) as physical symptoms from medical illness can inflate depression scores 1

Patients with Cognitive Impairment

Do not rely on PHQ-9 in patients with cognitive impairment as it loses accuracy in this population; instead, use clinician observation and collateral information from family/caregivers 5

High-Risk Groups Requiring Screening

Screen patients with: 1

• Other psychiatric disorders (anxiety, substance use)
• Family history of depression
• Chronic medical diseases
• Unemployment or lower socioeconomic status
• Recent major life events (bereavement, medical diagnosis, institutional placement)

Assess Functional Impairment

Document how symptoms interfere with work, relationships, self-care, and daily activities as functional impairment is crucial for determining diagnosis and severity 5, 1

• Moderate depression (PHQ-9 8-14): Expect mild to moderate functional impairment
• Severe depression (PHQ-9 ≥15): Expect moderate to marked functional impairment

Assess Comorbid Conditions

Evaluate for: 1

• Anxiety disorders (present in majority of depressed patients)
• Panic attacks
• Substance abuse
• Bipolar disorder (screen for history of manic/hypomanic episodes before diagnosing unipolar depression) 6

Obtain Collateral Information

Interview both patient and collateral sources (family, caregivers) separately as patients frequently minimize symptom severity, making collateral information essential for accurate diagnosis 5

Common Diagnostic Pitfalls to Avoid

• Do not rely solely on symptom counts; always assess functional impairment and 2-week duration requirement 5
• Do not diagnose depression based on screening scores alone; confirm with structured diagnostic interview 1
• Do not use screening tools designed for general populations in patients with significant cognitive impairment 5
• Do not attribute all somatic symptoms to medical illness in medically ill patients; depression commonly co-occurs with medical conditions 1