Can disease-specific questionnaires describe the effect of comorbidities on health-related quality of life in patients with COPD? A comparison of disease-specific and generic questionnaires in the COSYCONET cohort

Background and aim: Health-related quality of life (HRQL) assessment in COPD is important as an individual descriptive measure as well as an endpoint in clinical studies. This study compares HRQL assessment with the generic EQ-5D-3L and two disease-specific questionnaires (SGRQ-C and CAT) in a comprehensive spectrum of COPD disease grades with particular attention on comorbidities. Methods: Using data from 2,291 subjects participating in the German COPD cohort COSYCONET, mean HRQL scores in different GOLD grades were compared by linear regression models adjusting for low (≤3) vs. high (u003e3) number of comorbidities or a list of 33 self-reported comorbid conditions and age, sex, education, smoking status, BMI. Discriminative abilities of HRQL instruments were assessed by standardized mean differences. Results: All HRQL instruments considered were able to discriminate between COPD grades, with some limitations for the EQ-5D utility score in mild disease. The effect of high comorbidity on HRQL was reflected by both generic and disease-specific questionnaires. The EQ-5D utility put the highest weight on comorbidity while the SGRQ was less influenced by comorbidity but discriminated best between GOLD grades. Psychiatric disorders and peripheral artery disease showed the strongest negative associations with HRQL in all questionnaires. Conclusion: COPD-specific HRQL questionnaires can also reflect the negative effects of comorbid conditions on HRQL but to a smaller degree than generic instruments. Findings may support clinical assessment and choice of HRQL instrument in future studies.