Trends and predictors of asthma costs: results from a 10-year longitudinal study.

Research on asthma costs often focuses on estimating average asthma costs. Trends in asthma costs and patterns of medication use, especially for those who have been followed up and under treatment, have received much less attention. This study's objective was to document asthma costs over time for asthma patients who are enrolled in an asthma care programme in Singapore and to identify its predictors, using a 10-year longitudinal dataset.The study population comprised different cohorts of 939 asthma patients entering the programme at different times during 2004-2013. Average asthma costs were estimated and the trends over time examined graphically, within and across patient cohorts. Regression analyses were conducted to examine cost predictors, with a focus on the relationship between risk factors at programme enrolment and subsequent asthma costs.The results indicate that 10-year average annual asthma cost was GBP 341 per patient. The main drivers of costs were asthma medications and consultation fees. Use of combined inhaled corticosteroid/long-acting β-agonist medications increased over time, but this was accompanied by declines in controller drug use, doctor visits and total asthma drug costs. Obesity, smoking and asthma severity were the main predictors of subsequent asthma costs, especially for females.