PHQ-9 (Patient Health Questionnaire-9) Calculator

What is the PHQ-9?

The Patient Health Questionnaire-9 (PHQ-9) is a self-administered diagnostic tool used to screen for, diagnose, monitor, and measure the severity of depression. It consists of nine questions based on the nine DSM-IV criteria for depression, with each question scored from 0 (not at all) to 3 (nearly every day).

The PHQ-9 is widely used in primary care and other medical settings due to its brevity, ease of administration, and strong validation in clinical studies. It can be used both as an initial screening tool and to monitor treatment response over time.

Clinical Applications

The PHQ-9 serves several important clinical functions:

• Screening: Identifying patients who may have depression
• Diagnosis: Assisting in making a provisional diagnosis of depression
• Severity Assessment: Determining the severity of depressive symptoms
• Monitoring: Tracking changes in depression severity over time and in response to treatment
• Treatment Planning: Guiding decisions about the need for treatment and the type of intervention

Interpretation of PHQ-9 Scores

The total score on the PHQ-9 ranges from 0 to 27, with higher scores indicating more severe depression:

Diagnostic Algorithm

In addition to the total score, the PHQ-9 can be used to make a provisional diagnosis of major depressive disorder (MDD) using the following algorithm:

Major Depressive Disorder is suggested if:

• Five or more of the nine symptom criteria have been present at least "more than half the days" in the past two weeks
• One of the symptoms is depressed mood or anhedonia (questions #1 or #2)

Other Depressive Disorder is suggested if:

• Two, three, or four of the nine symptom criteria have been present at least "more than half the days" in the past two weeks
• One of the symptoms is depressed mood or anhedonia (questions #1 or #2)

Suicide Risk Assessment

Question #9 on the PHQ-9 asks about thoughts of death or self-harm. Any positive response to this question (score > 0) should trigger a more comprehensive suicide risk assessment, regardless of the total PHQ-9 score.

Patients who indicate any suicidal thoughts should be assessed for suicide risk immediately, including evaluation of risk factors, protective factors, and the need for immediate intervention or referral.

Functional Impact

The PHQ-9 includes an additional question (not scored) that assesses the functional impact of the reported symptoms:

"If you checked off any problems, how difficult have these problems made it for you to do your work, take care of things at home, or get along with other people?"

This functional impact question helps clinicians understand how the depressive symptoms are affecting the patient's daily life and can guide treatment decisions and priorities.

Limitations

While the PHQ-9 is a valuable tool, it has several limitations:

• It is a screening tool, not a definitive diagnostic test for depression
• It may not capture all aspects of depression or related conditions
• Cultural factors may influence how symptoms are reported and interpreted
• Some medical conditions can cause symptoms that overlap with depression
• The tool relies on self-reporting, which may be affected by recall bias or other factors

References

1. Kroenke K, Spitzer RL, Williams JB. The PHQ-9: validity of a brief depression severity measure. J Gen Intern Med. 2001;16(9):606-613.
2. Levis B, Benedetti A, Thombs BD. Accuracy of Patient Health Questionnaire-9 (PHQ-9) for screening to detect major depression: individual participant data meta-analysis. BMJ. 2019;365:l1476.
3. Arroll B, Goodyear-Smith F, Crengle S, et al. Validation of PHQ-2 and PHQ-9 to screen for major depression in the primary care population. Ann Fam Med. 2010;8(4):348-353.
4. Manea L, Gilbody S, McMillan D. Optimal cut-off score for diagnosing depression with the Patient Health Questionnaire (PHQ-9): a meta-analysis. CMAJ. 2012;184(3):E191-E196.