Validation of the Finnish ISAAC questionnaire on asthma against anti-asthmatic medication reimbursement database in 5-year-old children.

Background: Valid identification of childhood asthma at the population level for epidemiological purposes remains a challenge. We aimed at validating the Finnish version of the International Study of Asthma and Allergies in Childhood (ISAAC) questionnaire based on parental-reported childhood asthma.
Materials and Methods: The ISAAC questionnaire has been validated against anti-asthmatic medication reimbursement data of the Finnish Social Insurance Institution, being the gold standard, among 2236 5-year-old consecutively born children (1996-2004) carrying human leukocyte antigen (HLA)-conferred susceptibility to type 1 diabetes. Two combined questionnaire questions (any wheezing symptom or use of asthma medication during the preceding 12 months plus ever asthma; any wheezing symptom or use of asthma medication during the preceding 12 months plus ever doctor-diagnosed asthma) were validated against valid reimbursement with purchase of at least one anti-asthmatic medication during a 12-month period. The validity of the questionnaire was estimated as the sensitivity, specificity, positive predictive value, negative predictive value, and Youden's index.
Results: The sensitivity 0.98 [95% confidence interval (CI) = 0.92-0.99]; specificity 0.98 (95% CI = 0.97-0.98); negative predictive value 1.00 (95% CI = 1.00-1.00); and Youden's index 0.96 (95% CI = 0.96-0.96) were the same for each of the two sets of combined questions. The positive predictive value for the first combined question was 0.63 (95% CI = 0.55-0.71), while it was 0.64 (95% CI = 0.57-0.72) for the second combined question.
Conclusion: The Finnish ISAAC questionnaire was highly valid and is an acceptable instrument for the survey of the prevalence of parental-reported childhood asthma for epidemiological purposes.
(© 2010 Blackwell Publishing Ltd.)