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PHQ-9 Depression Severityの包括的な教育ガイドを準備中です。ステップバイステップの解説、数式、実例、専門家のヒントをお届けしますので、もうしばらくお待ちください。
The Patient Health Questionnaire-9 (PHQ-9) is the most widely used validated screening and severity measurement tool for major depressive disorder in both primary care and specialist mental health settings worldwide. Developed by Kroenke, Spitzer, and Williams from the PRIME-MD diagnostic instrument and published in the Journal of General Internal Medicine in 2001, the PHQ-9 directly mirrors the nine diagnostic criteria for major depressive disorder as defined by the DSM-IV and DSM-5. The nine items assess: anhedonia (loss of interest or pleasure in activities), depressed mood, sleep disturbance, fatigue or loss of energy, appetite disturbance, feelings of worthlessness or excessive guilt, difficulty concentrating, psychomotor changes (agitation or retardation), and suicidal ideation. Each item is scored on a 4-point Likert scale reflecting frequency over the past 2 weeks: 0 = not at all, 1 = several days, 2 = more than half the days, 3 = nearly every day. Total scores range from 0 to 27, corresponding to severity bands: 0–4 (minimal or no depression), 5–9 (mild depression), 10–14 (moderate depression), 15–19 (moderately severe depression), and 20–27 (severe depression). A score of 10 or above is the standard threshold for clinical action, with a sensitivity of 88% and specificity of 88% for major depressive disorder. Item 9 specifically asks about thoughts of self-harm or being better off dead, and any positive response requires immediate safety assessment regardless of the total score. The PHQ-9 is free to use, available in over 100 languages, takes approximately 3 minutes to complete, and is validated for monitoring treatment response — a reduction of 5 or more points is considered a clinically significant response.
PHQ-9 Total = sum of 9 items (each 0–3); 0–4=minimal, 5–9=mild, 10–14=moderate, 15–19=moderately severe, 20–27=severe depression; ≥10 = clinical action threshold
- 1Step 1 — Administer the questionnaire: Ask the patient to rate each of the 9 items for the past 2 weeks: 0=not at all, 1=several days, 2=more than half the days, 3=nearly every day.
- 2Step 2 — Item 1 (Anhedonia): 'Little interest or pleasure in doing things.'
- 3Step 3 — Item 2 (Mood): 'Feeling down, depressed, or hopeless.'
- 4Step 4 — Items 3–8: Sleep disturbance, fatigue, appetite change, low self-worth, concentration difficulties, psychomotor disturbance.
- 5Step 5 — Item 9 (Suicidality): 'Thoughts that you would be better off dead, or of hurting yourself in some way.' ANY score >0 on this item requires immediate safety assessment.
- 6Step 6 — Calculate total score: Sum all 9 item scores (0–27). Assign severity category.
- 7Step 7 — Interpret and act: Score 0–4: reassure; 5–9: watchful waiting, lifestyle advice; 10–14: structured psychological therapy (CBT/counselling); 15–19: antidepressants or high-intensity psychological therapy; 20–27: antidepressants + specialist referral; any suicidal ideation: immediate safety assessment and safeguarding.
Watchful waiting; psychoeducation; sleep hygiene; repeat PHQ-9 at 2–4 weeks
7 × 1 = 7. Below the 10-point action threshold. Monitor and review. Low-intensity psychological interventions (guided self-help) are first-line for PHQ-9 5–9.
Structured CBT referral or trial of SSRI antidepressant; follow-up in 2–4 weeks; safety-net for suicidality
Total = 13. Moderate depression threshold. NICE recommends high-intensity psychological therapy (CBT) and/or antidepressants. Confirm no suicidal ideation (item 9 = 0).
Do not discharge without risk assessment; consider same-day psychiatric review or crisis team referral
Item 9 scored ≥1 requires immediate safety assessment regardless of total. At PHQ-9 ≥20, specialist psychiatric input is indicated. Immediate referral pathways should be activated.
Continue current treatment; target PHQ-9 <5 (remission); reassess at 12 weeks
A ≥5-point reduction is the standard threshold for clinically meaningful response. PHQ-9 <5 = remission target. From PHQ-9 18 to 12 = 33% improvement = partial response; continue and re-evaluate.
Primary care annual depression screening for patients with chronic disease, significant life stressors, or previous depressive episodes, representing an important application area for the Phq9 in professional and analytical contexts where accurate phq9 calculations directly support informed decision-making, strategic planning, and performance optimization
Stepped care treatment matching in IAPT (Improving Access to Psychological Therapies) services to allocate appropriate therapy intensity, representing an important application area for the Phq9 in professional and analytical contexts where accurate phq9 calculations directly support informed decision-making, strategic planning, and performance optimization
Academic researchers and university faculty use the Phq9 for empirical studies, thesis research, and peer-reviewed publications requiring rigorous quantitative phq9 analysis across controlled experimental conditions and comparative studies, where accurate phq9 analysis through the Phq9 supports evidence-based decision-making and quantitative rigor in professional workflows
Occupational health services screening for work-related depression and monitoring return-to-work readiness, representing an important application area for the Phq9 in professional and analytical contexts where accurate phq9 calculations directly support informed decision-making, strategic planning, and performance optimization
Digital mental health platforms and mobile applications for remote depression monitoring and symptom tracking, representing an important application area for the Phq9 in professional and analytical contexts where accurate phq9 calculations directly support informed decision-making, strategic planning, and performance optimization
Bipolar Disorder Screening
{'title': 'Bipolar Disorder Screening', 'body': 'PHQ-9 screens for depressive episodes but does not assess for manic or hypomanic history, which is essential to identify bipolar disorder. Prescribing SSRIs to bipolar patients in a depressive episode without mood stabilisers can precipitate manic switching. Always screen for prior hypomanic/manic episodes before initiating antidepressants. The MDQ (Mood Disorder Questionnaire) can supplement PHQ-9 in this context.'}
Post-Natal Depression
{'title': 'Post-Natal Depression', 'body': 'The Edinburgh Postnatal Depression Scale (EPDS) is the standard validated tool for post-natal depression screening (weeks 4–6 post-delivery) because it de-emphasises somatic symptoms that are normal in the immediate post-natal period. PHQ-9 can be used but EPDS is preferred in this population. NICE recommends universal post-natal depression screening at 4–6 weeks and 3–4 months.'}
Depression in Older Adults
{'title': 'Depression in Older Adults', 'body': 'PHQ-9 has been validated in older adults (65+) but somatic item confounding by comorbidities is more pronounced. The Geriatric Depression Scale (GDS) was specifically designed for older adults and avoids somatic items. Cognitive impairment (which also affects concentration, fatigue, sleep) may inflate PHQ-9 scores — cognitive screening (e.g., MoCA) should accompany PHQ-9 assessment in elderly patients.'}
Depression in Chronic Physical Illness
{'title': 'Depression in Chronic Physical Illness', 'body': 'Depression prevalence is 2–3 times higher in patients with chronic conditions including diabetes, heart failure, COPD, and cancer. PHQ-9 ≥10 in medically ill patients is associated with worse functional outcomes, reduced treatment adherence, and higher mortality. All patients with significant chronic illness should be screened with PHQ-9 at least annually.'}
| Score | Severity | Recommended Action |
|---|---|---|
| 0–4 | Minimal/None | Reassure; monitor if persisting |
| 5–9 | Mild | Watchful waiting; psychoeducation; lifestyle; low-intensity therapy |
| 10–14 | Moderate | Structured psychological therapy (CBT); consider SSRI |
| 15–19 | Moderately Severe | High-intensity CBT + antidepressant (SSRI) |
| 20–27 | Severe | Antidepressant + urgent psychiatric referral; hospitalisation if risk |
| Item 9 ≥1 (any total) | Suicidal ideation | IMMEDIATE safety assessment; do not leave unattended |
What is the clinical action threshold for PHQ-9?
A PHQ-9 score of 10 or above is the standard clinical action threshold, with sensitivity and specificity of approximately 88% each for major depressive disorder. Below 10, the patient may have subthreshold depressive symptoms (5–9) requiring monitoring and low-intensity support. Above 10, active treatment (psychological therapy or medication) is indicated according to NICE CG90 guidelines.
How quickly should PHQ-9 be repeated during treatment?
NICE recommends repeat PHQ-9 at 2–4 weeks after starting antidepressants, as early response (defined as ≥20% reduction at 2–4 weeks) predicts eventual remission. For patients on psychological therapy (CBT), reassessment at 4–8 weeks is standard. Serial PHQ-9 monitoring every 4 weeks during active treatment phase is recommended. This is particularly important in the context of phq9 calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise phq9 computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What does a positive item 9 response mean?
Item 9 ('Thoughts that you would be better off dead or of hurting yourself') scoring ≥1 requires immediate clinical assessment, regardless of total PHQ-9 score. This includes a comprehensive risk assessment: ideation, plan, intent, access to means, previous attempts, protective factors, and social support. A safety plan must be created and documented. Never dismiss any positive response to item 9.
Can PHQ-9 be used for diagnosis of depression?
PHQ-9 is a screening and severity measurement tool, not a diagnostic instrument. A high score is not a diagnosis — it indicates high probability of depressive disorder and need for clinical assessment. Diagnosis requires a clinical interview assessing symptom duration (≥2 weeks), functional impairment, exclusion of organic causes (thyroid disease, anaemia, cancer), and differential diagnosis (bipolar disorder, grief reaction).
What is the PHQ-2 and when is it used?
The PHQ-2 comprises just the first two items of the PHQ-9: anhedonia and depressed mood. A PHQ-2 score ≥3 has 83% sensitivity for major depression and is used as an ultra-brief screening tool in busy primary care settings. Patients who screen positive on PHQ-2 should proceed to full PHQ-9 assessment.
Is PHQ-9 valid in medical illness and chronic pain patients?
PHQ-9 was primarily validated in ambulatory general medicine and psychiatry populations. Somatic items (fatigue, sleep disturbance, appetite change) may be elevated by medical illness rather than depression, potentially inflating PHQ-9 scores in patients with chronic conditions. The PHQ-9 cognitive subscale (items 1, 2, 5, 6, 7, 9) is sometimes used to reduce somatic confounding in medically ill patients.
What is the minimally important difference in PHQ-9 for treatment response?
A ≥5-point reduction in PHQ-9 from baseline is considered a clinically meaningful response. Remission is generally defined as PHQ-9 <5. Response without remission (PHQ-9 reduced ≥50% but still ≥5) indicates partial response and may warrant treatment augmentation, dose increase, or switch to alternative antidepressant. This is particularly important in the context of phq9 calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise phq9 computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
Can the PHQ-9 be self-administered by patients?
Yes — the PHQ-9 was designed for self-administration and is equally valid when completed by the patient without clinician administration. Patient self-completion in waiting rooms or via digital platforms (apps, online portals) allows efficient screening and monitoring. Self-administered PHQ-9 scores correlate well with clinician-administered versions in validation studies. This is particularly important in the context of phq9 calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise phq9 computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
プロのヒント
Always review all nine items individually, not just the total score. Items 1 (anhedonia) and 9 (suicidality) are clinically the most important: anhedonia is the core feature of major depressive disorder, and any positive suicidality response requires immediate action regardless of total score. For treatment monitoring, graph serial PHQ-9 scores against treatment dates — a visual trajectory is more informative than a single number.
ご存知でしたか？
The PHQ-9 was developed from the PRIME-MD (Primary Care Evaluation of Mental Disorders), a longer clinician-administered instrument, when researchers recognised that briefer self-report tools would dramatically improve depression detection rates in busy primary care settings. Since its publication in 2001, it has been translated into over 100 languages and cited in over 8,000 peer-reviewed publications — making it one of the most-cited psychiatric assessment tools in medical literature history.
参考文献
- ›Kroenke K, Spitzer RL, Williams JB — The PHQ-9: Validity of a Brief Depression Severity Measure (J Gen Intern Med 2001)
- ›NICE CG90 — Depression in Adults: Recognition and Management (2022 update)
- ›Manea L et al. — Optimal Threshold for PHQ-9 — Meta-analysis (Can J Psychiatry 2012)
- ›Spitzer RL et al. — Validation and Utility of the PRIME-MD Patient Health Questionnaire (JAMA 1999)
- ›LITFL PHQ-9 Depression Screening Reference