PHQ-9 is the Most Appropriate Tool for Assessing Low Mood and Possible Early Depression
For a patient presenting with low mood and possible early depression, use the Patient Health Questionnaire-9 (PHQ-9) as your primary assessment tool. This is a 9-item self-report scale that directly assesses symptoms of major depressive disorder according to DSM-IV criteria, making it the most practical and evidence-based choice for initial evaluation 1, 2.
Why the PHQ-9 is Superior
The PHQ-9 stands out among depression screening tools because it:
- Directly maps to DSM-IV diagnostic criteria for major depressive disorder, providing both screening and severity assessment in one instrument 1
- Takes less than 5 minutes to complete, making it highly practical for routine clinical use 3
- Has established cutoff scores that guide clinical decision-making: scores ≥8 indicate need for further evaluation, with moderate symptomatology at 8-14 and moderate-to-severe at 15-19 2
- Includes functional impairment assessment, which other tools may lack 1
Recommended Screening Algorithm
Step 1: Start with the 2-item PHQ-9 screen
- Ask about anhedonia: "Little interest or pleasure in doing things"
- Ask about depressed mood: "Feeling down, depressed or helpless"
- If the patient scores 0-1 on both items combined, no further screening is needed 1
Step 2: If score ≥2 on the 2-item screen, complete the full 9-item PHQ-9
- Only 25-30% of patients will need to complete the full questionnaire 2
- This two-step approach is more efficient than administering the full PHQ-9 to everyone
Step 3: Interpret the total score
- 1-7: None/mild symptomatology - monitor, no immediate intervention needed
- 8-14: Moderate symptomatology - seek consultation with psychology or psychiatry for diagnosis determination 1
- 15-19: Moderate-to-severe symptomatology - refer to psychology/psychiatry for diagnosis and treatment
- 20-27: Severe symptomatology - immediate referral to psychology/psychiatry 1
Critical Safety Consideration
Item 9 of the PHQ-9 assesses self-harm thoughts ("Thoughts that you would be better off dead or hurting yourself in some way"). If a patient endorses this item as occurring "more than half the days" or "nearly every day," this requires immediate risk assessment 2. However, do not omit this item from the questionnaire, as doing so artificially lowers the total score and weakens predictive validity 2.
Comparison with Other Tools
While other depression screening instruments exist (Beck Depression Inventory, Hamilton Rating Scale for Depression, Hospital Anxiety and Depression Scale, Center for Epidemiological Studies Depression Scale), they have significant limitations for initial assessment 1:
- BDI (21 items): Longer and requires scores ≥20 to suggest clinical depression, making it less sensitive for early/mild depression
- HAM-D (17 items): Requires clinician administration rather than self-report, making it impractical for routine screening
- HADS (14 items): Designed primarily for medical populations to avoid confounding with physical symptoms
- CES-D (20 items): Longer and designed for epidemiological studies rather than clinical screening
Special Populations
For elderly patients: Consider the Geriatric Depression Scale (GDS-15) as an alternative, as depression can be more difficult to detect in older adults and the GDS focuses on affective symptoms rather than somatic complaints 1. However, the PHQ-9 remains appropriate for most older adults.
When to Screen
Screen at 2:
- Initial visit/diagnosis
- Regular intervals during treatment
- Changes in disease or treatment status
- Post-treatment transition
- Any time clinical suspicion arises
The PHQ-9's combination of brevity, diagnostic alignment, established validity across diverse populations 4, and clear clinical cutoffs makes it the optimal first-line tool for assessing low mood and possible early depression in routine practice.