Performance of the PHQ-9 across conditions and comorbidities: Findings from the Veterans Outcome Assessment survey.

Background: The items of the Patient Health Questionnaire-9 (PHQ-9) represent the criterion symptoms for DSM-IV major depression. This study evaluated the extent to which the PHQ-9 functions as a patient-reported outcome measure (PROM) specific to patients with major depressive disorder.
Method: Data were from the Veterans Outcome Assessment survey for 8848 patients beginning treatment in VA general mental health clinics, including 5754, re-surveyed after 3 months. The PHQ-9's performance as a PROM was evaluated by comparing rank order correlations between both initial scores and improvements over 3 months between the PHQ-9 and several transdiagnostic PROMs across a range of diagnoses and comorbidities. Performance of PHQ-9-related patient-reported outcome-based performance measures (PROM-PM) were evaluated by comparing rates of response and remission across patient groups.
Results: Correlations between the PHQ-9 and transdiagnostic measures were significant and comparable in magnitude across a range of diagnoses and for cases with depression with or without comorbidities. Rates of response and remission were comparable across most patient groups.
Limitations: Limitations include use of clinical diagnoses as recorded in health records, and the relatively short time between assessments.
Conclusions: In these settings, the PHQ-9 functions more as a general measure of symptoms or distress than as a disease-specific scale. This supports its use as a PROM for patients beyond those with major depression, including those with related diagnoses and those with comorbidities, and use of related PROM-PMs in clinical settings where diagnoses may not be precise and comorbidities may be common.
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