Margarethe E Wacker, Katharina Kitzing, Rudolf A Jörres, Reiner Leidl, Holger Schulz, Stefan Karrasch, Annika Karch, Armin Koch, Claus F Vogelmeier, Rolf Holle

Although patients with COPD often have various comorbidities and symptoms, limited data are available on the contribution of these aspects to health care costs. This study analyzes the association of frequent comorbidities and common symptoms with the annual direct and indirect costs of patients with COPD. Self-reported information on 33 potential comorbidities and symptoms (dyspnea, cough, and sputum) of 2,139 participants from the baseline examination of the German COPD cohort COSYCONET was used. Direct and indirect costs were calculated based on self-reported health care utilization, work absence, and retirement. The association of comorbidities, symptoms, and COPD stage with annual direct/indirect costs was assessed by generalized linear regression models. Additional models analyzed possible interactions between COPD stage, the number of comorbidities, and dyspnea. Unadjusted mean annual direct costs were €7,263 per patient. Other than COPD stage, a high level of dyspnea showed the strongest driving effect on direct costs (+33%). Among the comorbidities, osteoporosis (+38%), psychiatric disorders (+36%), heart disease (+25%), cancer (+24%), and sleep apnea (+21%) were associated with the largest increase in direct costs (p<0.01). A sub-additive interaction between advanced COPD stage and a high number of comorbidities reduced the independent cost-driving effects of these factors. For indirect costs, besides dyspnea (+34%), only psychiatric disorders (+32%) and age (+62% per 10 years) were identified as significant drivers of costs (p<0.04). In the subsequent interaction analysis, a high number of comorbidities was found to be a more crucial factor for increased indirect costs than single comorbidities. Detailed knowledge about comorbidities in COPD is useful not only for clinical purposes but also to identify relevant cost factors and their interactions and to establish a ranking of major cost drivers. This could help in focusing therapeutic efforts on both clinically and economically important comorbidities in COPD.