At what Patient Health Questionnaire (PHQ)-9 score should a selective serotonin reuptake inhibitor (SSRI) be started for a patient with depressive symptoms?

PHQ-9 Thresholds for Starting SSRI Treatment

Consider starting an SSRI when the PHQ-9 score is ≥8, with mandatory psychiatric referral and high-intensity treatment (including pharmacotherapy) for scores ≥15. 1, 2

Algorithmic Approach to Treatment Based on PHQ-9 Score

PHQ-9 Score 1-7 (Minimal Depression)

• Do not initiate SSRI therapy at this level, as symptoms typically respond to supportive care and may resolve spontaneously 3
• Provide patient education about depression and normal stress responses 3
• Verify adequate coping skills and social support systems 3
• Schedule reassessment with repeat PHQ-9 at 3,6, and 12 months or during times of transition 3
• Critical exception: If item 9 (self-harm) is endorsed at any frequency, immediate psychiatric evaluation is required regardless of total score 3

PHQ-9 Score 8-14 (Moderate Depression)

• SSRIs may be initiated as part of a treatment plan that includes low-intensity interventions 2, 4
• First-line options include:
  • Individually guided self-help based on cognitive behavioral therapy with behavioral activation 2, 4
  • Structured physical activity programs 2, 4
  • Pharmacologic treatment (SSRIs) as appropriate based on clinical judgment and patient preference 4
• Refer to psychology or psychiatry for formal diagnostic confirmation 4
• Rule out medical causes: check thyroid function, complete metabolic panel, CBC, vitamin B12/folate, and review medications for mood-altering effects (interferon, corticosteroids, beta-blockers) 4
• Assess duration of symptoms, sociodemographic risk factors, and degree of functional impairment 4

PHQ-9 Score 15-27 (Moderately Severe to Severe Depression)

• Immediate referral to psychiatry/psychology is mandatory with high-intensity interventions including SSRIs 2, 4
• SSRIs are equally effective in severe depression compared to tricyclic antidepressants 5, 6
• High-intensity psychological therapy using treatment manuals with cognitive change and behavioral activation should accompany pharmacotherapy 2
• Facilitate safe environment with one-to-one observation if self-harm risk is present 4

Evidence Supporting the PHQ-9 ≥8 Cutoff

The ASCO guideline specifically recommends a cutoff score of ≥8 (rather than the traditional ≥10) based on diagnostic accuracy studies in cancer outpatients and meta-analysis data, which demonstrates improved sensitivity for detecting clinically significant depression 1, 2. This lower threshold captures patients with moderate depressive symptomatology who have functional impairment ranging from mild to moderate and require active treatment 2, 4.

Critical Safety Considerations

• Never omit item 9 regarding self-harm thoughts when administering the PHQ-9, as this artificially lowers scores and misses critical risk information 2, 4, 3
• Any endorsement of self-harm ideation requires immediate emergency psychiatric evaluation regardless of total PHQ-9 score 2, 4, 3
• The frequency and specificity of self-harm thoughts are most important for risk assessment 1, 4

Phased Screening Approach

1. First step: Identify presence/absence of pertinent history or risk factors (prior mood disorders, comorbid anxiety, substance use, chronic medical illness) 1, 4
2. Second step: Administer the first two PHQ-9 items assessing anhedonia and depressed mood 1
3. Third step: If either item scores ≥2, complete the remaining 7 items of the PHQ-9 1, 2

Special Population Considerations

• Cognitive impairment: The PHQ-9 loses accuracy in patients with cognitive impairment; use alternative assessment methods 2, 4
• Older adults: Depression detection is particularly challenging and may require additional clinical judgment or the Geriatric Depression Scale 1, 4
• Cultural sensitivity: Use culturally sensitive assessments when possible and tailor evaluation for patients with learning disabilities 1, 2, 4

Common Pitfalls to Avoid

• Undertreatment: A score of 8-14 requires active treatment, not observation alone 4
• Overtreatment: Do not initiate SSRIs for scores <8, as this represents overtreatment of mild symptoms 3
• Incomplete screening: Always complete the full 9-item PHQ-9 if initial 2-item screen is positive 2, 4
• Missing medical causes: Always rule out thyroid dysfunction, medication effects, and other medical causes before diagnosing primary depression 4

Monitoring Treatment Response

The PHQ-9 is a validated tool for gauging response to SSRI treatment, with an expected decrease of approximately 10 points over 12 weeks in responders (effect size -1.85) 7. Reassess with PHQ-9 at regular intervals during treatment 4.