Medications containing inhaled corticosteroids (ICS), blood eosinophils and decline in lung function (FEV1) in a cohort of patients with Chronic Obstructive Pulmonary Disease (COPD) identified in the Clinical Practice Research Datalink (CPRD) database

Trial description: This study aims to assess the relationship between ICS and lung function decline, particularly forced expiratory volume in one second (FEV1), in a primary care COPD population in the United Kingdom (UK) with pre-defined high or low blood eosinophil levels. This is a retrospective cohort study, which will use routinely collected primary care electronic health records (EHR) from the CPRD-Global Initiative for Chronic Obstructive Lung Disease (GOLD) database and linked data from hospital episode statistics (HES) in the UK. Subjects with COPD will be identified based on validated diagnosis of COPD from 01 January 2004 to 29 February 2016. The date of first measurement of FEV1 after the subject’s first COPD diagnosis, up-to-standard (UTS) data and current registration date in eligible subjects will be considered the index date. Subjects will be followed from the index date until 29 February 2016 (end of linked data availability) or earlier, if the subject died or transferred out of the general practice (GP). The cohort studied will comprise of approximately 61,000 (based on feasibility) eligible subjects with a record for diagnosis of COPD aged 35 years or older, who are smokers or ex-smokers with at least 2 spirometry measurements in their data at least 6 months apart, and have at least one eosinophil measurement recorded in their data. The mean follow-up period is expected to be about 6.5 years. Based on sample size calculation, to evaluate a difference of 5 milliliter per year (mL/year) between the mean rates of decline in two groups of ICS or non-ICS users, 4,750 and 2,102 subjects will be required.