Socioeconomic inequalities in adherence to inhaled maintenance medications and clinical prognosis of COPD

BACKGROUND: Low socioeconomic status has been associated with adverse outcomes in chronic obstructive pulmonary disease (COPD), but population-based data are sparse. We examined the impact of education, employment, income, ethnicity, and cohabitation on the risk of suboptimal adherence to inhaled medication, exacerbations, acute admissions, and mortality among COPD patients.

METHODS: Using nationwide healthcare registry data we identified 13,369 incident hospital clinic outpatients with COPD during 2008-2012. We estimated medication adherence as proportion of days covered (PDC) one year from first contact. With Poisson regression we computed adjusted relative risks (aRR) of poor adherence and non-use. With Cox regression we calculated adjusted hazard ratios (aHR) of clinical outcomes.

RESULTS: 32% were poor adherers (PDC<0.8) and 5% non-users (PDC = 0). Analyses showed a higher risk of poor adherence among unemployed (aRR1.36, 95% CI 1.20-1.54), low income patients (aRR = 1.07, 95% CI 1.00-1.16), immigrants (aRR = 1.29, 95% CI 1.17-1.44), and patients living alone (aRR = 1.17, 95% CI 1.11-1.24). Similarly, non-use was associated with unemployment (aRR = 2.75, 95% CI 2.09-3.62), low income (aRR = 1.37, 95% CI 1.10-1.70), immigrant status (aRR = 1.56, 95% CI 1.17-2.08), and living alone (aRR = 1.53, 95% CI 1.30-1.81). Low education was associated with exacerbations (aHR = 1.21, 95% CI 1.10-1.35) and admissions (aHR = 1.22, 95% CI 1.07-1.38). Low income was associated with admissions (aHR = 1.20, 95% CI 1.09-1.32), and death (aHR = 1.11, 95% CI 0.99-1.25). The unemployed and those living alone had lower exacerbation-risk but higher mortality-risk.

CONCLUSIONS: In Denmark, health equity is a stated priority in a public health care system. Nevertheless, there are substantial socioeconomic inequalities in COPD treatment and outcomes.