What is the Patient Health Questionnaire-9 (PHQ-9)?

What is the Patient Health Questionnaire-9 (PHQ-9)?

The PHQ-9 is a 9-item self-report screening tool that assesses the nine DSM-IV criteria for major depressive disorder, with each item scored from 0 (not at all) to 3 (nearly every day), yielding a total score of 0-27 that quantifies depression severity. 1

Core Components and Structure

The PHQ-9 directly maps to the diagnostic criteria for major depressive disorder, covering the following domains: 1

• Depressed mood (feeling down, depressed, or hopeless)
• Anhedonia (little interest or pleasure in doing things)
• Sleep disturbances
• Fatigue or loss of energy
• Appetite changes
• Feelings of worthlessness or guilt
• Concentration difficulties
• Psychomotor agitation or retardation
• Suicidal ideation (thoughts of self-harm or being better off dead)

Each symptom is rated based on frequency over the past 2 weeks, with response options of 0 (not at all), 1 (several days), 2 (more than half the days), or 3 (nearly every day). 2

Score Interpretation and Clinical Thresholds

The PHQ-9 provides specific cutoff scores that guide clinical decision-making: 1, 3

• 1-7: Minimal or no depression
• 8-14: Moderate depressive symptomatology
• 15-19: Moderately severe depression
• 20-27: Severe depression

The American Society of Clinical Oncology recommends a cutoff score of 8 (rather than the traditional 10) based on diagnostic accuracy studies in cancer outpatients and meta-analysis data. 1, 3 At this threshold, the PHQ-9 demonstrates a sensitivity of 88% and specificity of 88% for major depression when using a cutoff of 10. 2

Phased Screening Approach

The most efficient implementation uses a two-step process: 1, 3

1. Initial screening: Administer only the first two items (depressed mood and anhedonia)
2. Full assessment: If either item scores ≥2 (present more than half the days), complete the remaining 7 items
3. Estimated efficiency: Only 25-30% of patients require the full 9-item questionnaire 1

Clinical Actions Based on Scores

For scores 8-14 (moderate depression): Initiate low-intensity interventions including guided self-help based on cognitive behavioral therapy, structured physical activity programs, or consider pharmacologic treatment. 3, 4

For scores ≥15 (moderately severe to severe depression): Immediate referral to psychology and/or psychiatry for formal diagnosis and treatment is mandatory. 3, 4

For any positive response to item 9 (self-harm): Immediate referral for emergency psychiatric evaluation is required regardless of total score. 3, 5

Critical Safety Considerations

Never omit item 9 regarding self-harm thoughts, as doing so artificially lowers scores and misses critical risk information. 1, 3 The frequency and specificity of self-harm thoughts are most important for risk assessment, and individuals rarely endorse this item in isolation—it typically occurs alongside multiple other symptom endorsements. 1

Validated Uses Beyond Screening

The PHQ-9 serves multiple clinical functions: 2, 6

• Diagnostic screening for major depressive disorder
• Severity assessment to guide treatment intensity
• Treatment monitoring with a minimal clinically important difference of 5 points on the 0-27 scale 6
• Outcome measurement with excellent responsiveness to treatment (effect size of -1.3 at 3 and 6 months) 6

Timing of Administration

Administer the PHQ-9 at: 4

• Initial diagnosis or start of treatment
• Regular intervals during treatment
• 3,6, and 12 months after treatment completion
• Times of personal transition or family crisis
• When approaching end of life in palliative care settings

Important Limitations and Special Populations

The PHQ-9 loses accuracy in patients with cognitive impairment, requiring alternative assessment methods such as informant-based tools. 4, 5

For elderly patients, the Geriatric Depression Scale (GDS-15 or GDS-30) may be more appropriate, as it focuses on affective symptoms and excludes somatic items that may be confounded by medical illness. 1, 5

For medically ill or cancer patients, the Hospital Anxiety and Depression Scale (HADS) may be preferable as it excludes physical symptom items that could be attributed to medical conditions rather than depression. 1, 3

Essential Pre-Diagnostic Considerations

Before diagnosing primary major depressive disorder based on PHQ-9 scores, rule out medical and substance-induced causes: 3, 5

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