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

Abstract 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.