Inhaled steroids and mortality in COPD: bias from unaccounted immortal time.
A recent observational study, which suggested that inhaled corticosteroids (ICS) with or without long-acting bronchodilators are effective at reducing all-cause mortality in chronic obstructive pulmonary disease (COPD) patients, may be subject to immortal time bias. This bias was assessed using a population-based cohort of 3,524 newly treated COPD patients from Saskatchewan, Canada, observed from 1990-1999. Regular users of bronchodilators or ICS were followed for 3 yrs, during which time 860 deaths occurred. Cox's proportional hazards model was used to compare the hierarchical intention-to-treat approach employed in the recent study, a technique subject to bias from two sources of immortal time, with the conventional intention-to-treat approach and the according-to-treatment approach. The adjusted rate ratio of death using the hierarchical intention-to-treat approach was 0.66 (95%) confidence interval (CI) 0.57-0.76) for ICS use relative to bronchodilator use, compared with 0.75 (95% CI 0.62-0.90) with the conventional intention-to-treat approach. Conversely, the rate ratio was 0.94 (95% CI 0.81-1.09) with the according-to-treatment approach, which accounts for both sources of immortal time. In this study, regular inhaled corticosteroid use in chronic obstructive pulmonary disease was not found to reduce all-cause mortality. Suggestion of this benefit from a previous observational study is the result of bias from unaccounted immortal time in its cohort design and analysis.
Suissa
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Division of Clinical Epidemiology, Royal Victoria Hospital, McGill University Health Centre, Montreal, Québec, Canada. samy.suissa@clinepi.mcgill.ca
D000280:Administration, Inhalation; D000336:Aerosols; D000368:Aged; D015982:Bias; D001993:Bronchodilator Agents / Q000008:administration & dosage / Q000627:therapeutic use; D015331:Cohort Studies; D016208:Databases, Factual; D005260:Female; D005938:Glucocorticoids / Q000008:administration & dosage* / Q000627:therapeutic use; D006801:Humans; D008297:Male; D019370:Observation; D016016:Proportional Hazards Models; D029424:Pulmonary Disease, Chronic Obstructive / Q000188:drug therapy* / Q000401:mortality*; D012107:Research Design; D013997:Time Factors
D000336:Aerosols; D001993:Bronchodilator Agents; D005938:Glucocorticoids