Abstract
Purpose: Validated measures of asthma and eczema at the population level remain a challenge. Our aim was to ascertain if register-based information on asthma/eczema medication can function as a proxy for an asthma/eczema diagnosis and to validate register-based asthma diagnoses.
Methods: Information was requested on all 0-45 year old individuals with reported asthma/eczema medication and/or diagnoses in the Swedish Prescribed Drug Register and National Patient Register, between July 2005 and December 2009 (N=250,691). Medical records for 1,952 randomly selected individuals were reviewed to estimate the proportion of individuals with 1) asthma/eczema medication that fulfilled predefined criteria of asthma/eczema (positive predictive value, PPV); 2) a register-based asthma diagnosis verified as asthma by set criteria.
Results: PPV for asthma by predefined criteria ranged between 0.75 (95% CI: 0.70-0.78) to 0.94 (95% CI: 0.91-0.96), depending on age-group. In pre-school children, PPV for asthma in combination with obstructive bronchitis was 0.87 (95% CI: 0.83-0.90) and PPV for eczema was estimated to 0.45 (95% CI: 0.38-0.51). Eighty percent of children 0-4.5 years and 99% of children >4.5-17 years with a register-based diagnosis of asthma were verified as asthmatics.
Conclusion: Asthma medication is a suitable proxy for asthma in older children and adults; the same approach is insufficient for eczema. This validation study of two Swedish registers opens for future large nation-wide register-based studies on asthma.
