Validation of asthma and eczema in population‐based Swedish drug and patient registers

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 1952 randomly selected individuals were reviewed to estimate the proportion of individuals with the following: (1) asthma/eczema medication that fulfilled predefined criteria of asthma/eczema (positive predictive value (PPV)) and (2) a register‐based asthma diagnosis verified as asthma by predefined criteria. Results Positive predictive value 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. Copyright © 2013 John Wiley & Sons, Ltd.