The Patient Health Questionnaire-9 (PHQ-9) demonstrates validity as an instrument to measure depression in patients with chronic obstructive pulmonary disease (COPD), according to the results of a study published in the Journal of Affective Disorders.
Depression in patients with COPD is common, with prevalence estimates ranging from 15% to 40%. It is associated with higher symptom burden and lower quality of life, worse functional capacity, increased exacerbations of COPD, and higher mortality. Thus, there is a need to assess patients with COPD routinely for depression and to identify valid assessment tools.
Michael Schuler, of the University of Wurzburg, Department of Medical Psychology and Psychotherapy, Medical Sociology and Rehabilitation Sciences, Wurzburg, Germany, and colleagues conducted a secondary analysis of 561 patients with COPD who filled out the PHQ-9 questionnaire at the beginning, end, and 3, 6, 9, and 12 months after pulmonary inpatient rehabilitation.
The PHQ-2 was used as a comparator. They used structural equation modeling to examine factorial validity and measurement invariance between gender, Global Initiative on Chronic Obstructive Lung Disease (GOLD) severity group, and over time. They assessed concordance using Cohen’s Kapp, Yules Y, and positive and negative agreement.
Although concordance between the 2 instruments was substantial, more patients were classified as having clinically relevant depression by PHQ-9 (31.7%) than by PHQ-2 (26.2%) at the start of rehabilitation. Both measures showed a significant decline in depression rates after rehabilitation. Twelve months after the end of pulmonary rehabilitation, the proportion of patients with depression was still lower than at therapy initiation. Although mean changes were low for all patients, they were high for patients with clinically relevant depression at baseline according to the results of both the PHQ-9 and PHQ-2. Reliability was high for both PHQ-9 (composite reliability=0.94) and PHQ-2 (composite reliability=0.89).
The investigators note that the study has several limitations. As this is a secondary analysis of a study with other primary research questions, no gold standard to assess depression was used, and the diagnostic accuracy of both PHQ-2 and PHQ-9 is not clear. Furthermore, there were few patients in the GOLD-IV group, so the GOLD-III and GOLD-IV groups were combined for this analysis.
Nonetheless, the researchers conclude that the PHQ-9 demonstrated good factorial validity, high reliability, as well as measurement invariance among patient groups and time points. They suggest that future studies should examine the diagnostic accuracy for both instruments in patients with COPD.
Schuler M, Strohmayer M, Mühlig S, et al. Assessment of depression before and after inpatient rehabilitation in COPD patients: Psychometric properties of the German version of the Patient Health Questionnaire (PHQ-9/PHQ-2). J Affect Disord. 2018;232:268-275.