Monitoring Depression Treatment Outcomes With the Patient Health Questionnaire-9

TLDR

Effective treatment of depression requires regular follow‑up and symptom monitoring, yet no efficient method for assessing treatment outcome exists. This study examined the responsiveness, reproducibility, and minimal clinically important difference of the PHQ‑9 in 434 older adults enrolled in the IMPACT late‑life depression trial. PHQ‑9 scores were tracked over six months, compared to SCL‑20 scores and two structured diagnostic interviews, and test‑retest reliability and minimal clinically important difference were evaluated in a subsample completing the questionnaire twice within seven days. The PHQ‑9 accurately distinguished persistent, partially remitted, and fully remitted depression, demonstrated excellent test‑retest reliability, a 5‑point minimal clinically important difference, and proved responsive and brief enough to be useful in both clinical care and research.

Abstract

Although effective treatment of depressed patients requires regular follow-up contacts and symptom monitoring, an efficient method for assessing treatment outcome is lacking. We investigated responsiveness to treatment, reproducibility, and minimal clinically important difference of the Patient Health Questionnaire-9 (PHQ-9), a standard instrument for diagnosing depression in primary care.This study included 434 intervention subjects from the IMPACT study, a multisite treatment trial of late-life depression (63% female, mean age 71 years). Changes in PHQ-9 scores over the course of time were evaluated with respect to change scores of the SCL-20 depression scale as well as 2 independent structured diagnostic interviews for depression during a 6-month period. Test-retest reliability and minimal clinically important difference were assessed in 2 subgroups of patients who completed the PHQ-9 twice exactly 7 days apart.The PHQ-9 responsiveness as measured by effect size was significantly greater than the SCL-20 at 3 months (-1.3 versus -0.9) and equivalent at 6 months (-1.3 versus -1.2). With respect to structured diagnostic interviews, both the PHQ-9 and the SCL-20 change scores accurately discriminated patients with persistent major depression, partial remission, and full remission. Test-retest reliability of the PHQ-9 was excellent, and its minimal clinically important difference for individual change, estimated as 2 standard errors of measurement, was 5 points on the 0 to 27 point PHQ-9 scale.Well-validated as a diagnostic measure, the PHQ-9 has now proven to be a responsive and reliable measure of depression treatment outcomes. Its responsiveness to treatment coupled with its brevity makes the PHQ-9 an attractive tool for gauging response to treatment in individual patient care as well as in clinical research.