Clinical characteristics, mortality rates and causes of death in non-exacerbating COPD patients. A longitudinal cohort analysis of UK primary care data

A subset of COPD patients belong to a non-exacerbating phenotype with poorly understood characteristics and prognosis. We investigated clinical characteristics, mortality rates and causes of death of non-exacerbating compared to exacerbating COPD patients. We used data from the Clinical Practice Research Datalink (CPRD), linked to Hospital Episode Statistics and Office for National Statistics mortality data. We included COPD patients from UK primary practices with at least 3 years of baseline information. We compared baseline characteristics, mortality rates (hazard ratios (HR) from adjusted Cox regression analyses) and causes of death in non-exacerbating compared to exacerbating COPD patients. Among 67,516 patients, 17.3% did not exacerbate during the 3 year baseline period. Non-exacerbators were more likely to be male (63.3 vs 52.4%, p<0.001) and less likely to have a history of asthma (33.9 vs 43.6%, p<0.001) and FEV1 <50% (23.7 vs 31.8%) than exacerbators. Adjusted HR for mortality in non-exacerbators compared to exacerbators was 0.62 (95%CI 0.56-0.70) in the first year of follow-up and 0.87 (95%CI 0.83-0.91) thereafter. Respiratory causes of death were more common among exacerbating patients (44.5 vs 32.7%) but non-exacerbators died more often of malignancies (32.0 vs 25.3%) and cardiovascular diseases (30.2 vs 25.9%). In our primary care COPD cohort, almost one in five had no exacerbations and showed distinct clinical characteristics and lower mortality rates. These non-exacerbators were equally likely to die of respiratory, malignant or cardiovascular disease, whilst respiratory causes of death predominated in exacerbators.