Validation of asthma and eczema in population-based Swedish drug and patient registers
Correspondence to: A. K. Örtqvist, Department of Medical Epidemiology and Biostatistics, PO Box 281, Karolinska Institutet, SE-171 77, Stockholm, Sweden. E-mail: email@example.com
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.
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.
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.
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.