title: Validation of asthma and eczema in population-based Swedish drug and patient registers.
abstract: OBJECTIVE
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Anne K
authors.initials: AK
authors.lastname: Örtqvist
authors.forename: Cecilia
authors.initials: C
authors.lastname: Lundholm
authors.forename: Björn
authors.initials: B
authors.lastname: Wettermark
authors.forename: Jonas F
authors.initials: JF
authors.lastname: Ludvigsson
authors.forename: Weimin
authors.initials: W
authors.lastname: Ye
authors.forename: Catarina
authors.initials: C
authors.lastname: Almqvist
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use*; D001249:Asthma / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D001991:Bronchitis / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D003879:Dermatologic Agents / Q000627:therapeutic use*; D004485:Eczema / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012042:Registries / Q000706:statistics & numerical data; D013548:Sweden / Q000453:epidemiology; D055815:Young Adult
chemical_list: D018927:Anti-Asthmatic Agents; D003879:Dermatologic Agents
keywords: allergic diseases; asthma outcome research; asthma pharmacology; disease proxy; nationwide; pharmacoepidemiology; prescription prevalence