Depression as Measured by PHQ-9 Versus Clinical Diagnosis as an Independent Predictor of Long-Term Mortality in a Prospective Cohort of Medical Inpatients.

Background: Depression has been associated with higher rates of mortality in medical patients. The aim of the study was to evaluate the impact of depression in medical inpatients on the rate of mortality during a prolonged follow-up period.

Method: This is a prospective follow-up study of a cohort of medical inpatients assessed during 1997-1998 in medical and surgical units at a tertiary university hospital in Spain and followed-up for a period ranging between 16.5 and 18 years. Eight hundred three patients were included; 420 (52.3%) were male, and the mean (SD) age was 41.7 (13.8) years. Main outcome was death for any cause during follow-up. The original full Patient Health Questionnaire (PHQ) was administered at baseline as self-report from which the PHQ-9 was derived. Depressive disorders were assessed using PHQ-9 and a structured clinical interview (Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Revised Third Edition).

Results: Depressive disorders as defined by PHQ-9 were detected in 206 patients (25.7%), 122 (15.2%) of them fulfilling criteria for major depression. During follow-up, 152 patients (18.9%) died. A PHQ score indicating the presence of major depressive disorder predicted increased mortality (hazard ratio [HR], 2.44; 95% CI, 1.39-4.29), even after adjusting for important demographic and clinical variables. Similarly, the PHQ-9 score as a continuous measure of depression severity predicted increased mortality (HR, 1.06; 95% CI, 1.02-1.10). Results were similar for clinical interview diagnoses of major depression (HR, 2.07; 95% CI, 1.04-4.09).

Conclusions: Medical inpatients with a PHQ depressive disorder had a nearly 2-fold higher risk of long-term mortality, even after adjustment for several confounders. Depression severity as represented by the PHQ-9 score was also a risk factor.