PHQ-9 (Patient Health Questionnaire)

The PHQ-9 has excellent psychometric properties: sensitivity of 88% and specificity of 88% for major depression at a cutoff of 10. The area under the ROC curve is 0.95. It has been validated in primary care, specialty clinics, and community samples across diverse populations and languages.

A score of 10 or above is the standard threshold for clinically significant depression requiring treatment. However, a formal diagnosis of major depressive disorder requires: at least 5 symptoms present most days for at least 2 weeks, including either depressed mood (item 2) or anhedonia (item 1), confirmed by clinical interview.

For screening: at initial visit and annually. For monitoring treatment: every 2-4 weeks during acute treatment, monthly during continuation phase. A score reduction of 50% or more indicates clinical response. A score below 5 indicates remission. Serial scores guide treatment decisions.

Any score above 0 on item 9 requires immediate follow-up. Ask directly about suicidal intent, plan, access to means, and protective factors. Use a structured safety assessment (Columbia Suicide Severity Rating Scale). Implement appropriate safety measures. A positive item 9 does not automatically mean the patient is at imminent risk but must always be evaluated.

The PHQ-9 is a screening tool, not a diagnostic instrument. A positive screen (score >=10) has an ~88% probability of major depression but requires confirmation with a clinical interview that assesses duration, functional impairment, exclusion of bipolar disorder, substance use, and medical conditions that mimic depression.

0-4: Minimal (no treatment), 5-9: Mild (watchful waiting), 10-14: Moderate (psychotherapy and/or medication), 15-19: Moderately severe (medication and/or psychotherapy), 20-27: Severe (medication + psychotherapy, possible hospitalization). These categories guide the intensity of the treatment plan.

The PHQ-2 uses only the first 2 items (anhedonia and depressed mood) as an ultra-brief screen. If the PHQ-2 score is >=3, the full PHQ-9 is administered. The PHQ-2 has 97% sensitivity but lower specificity (67%), making it an excellent initial screen. The PHQ-9 provides severity grading and monitoring capability.

The PHQ-9 has been validated for adolescents ages 12-17, though the PHQ-A (adolescent version) is preferred as it includes additional questions. For children under 12, other instruments are used (Children's Depression Inventory, CDRS-R). The scoring and interpretation in adolescents are similar to adults.

Yes, the PHQ-9 is in the public domain and is free to use without permission. It was developed with public funding (NIMH) and the authors specifically made it freely available. It can be reproduced, translated, and used in clinical practice, research, and electronic health records without copyright restrictions.