Objective: To validate, for use in asthma prevalence studies, the asthma module of the standardized written questionnaire developed for use in the International Study of Asthma and Allergies in Childhood, establishing the score and cut-off point that would identify asthmatic adults. Methods: We interviewed 78 adult outpatients (40 adult asthmatics and 38 age-matched and gender-matched controls) using the asthma module of the International Study of Asthma and Allergies in Childhood questionnaire, which is composed of questions related to eight dichotomous features of asthma. We determined the score and cut-off point required to accurately identify asthmatic adults, calculating sensitivity, specificity and Youden index. The method was validated against the clinical and functional diagnosis of asthma. The reproducibility of individual questions was evaluated by conducting second interviews with half of the patients some weeks later. Results: The score ranged from 0 to 14 points. A score = 5 allowed patients with asthma to be distinguished from those without (sensitivity = 93%; specificity = 100%; Youden index = 0.93). Most questions presented satisfactory reproducibility in the second interviews conducted after 48.2 ± 11.1 days (kappa and weighted kappa ranging from 0.43 to 1.00 for individual questions). Conclusion: For studies of adult asthma prevalence, the determination/validation of a cut-off point allows an alternative interpretation of the information gathered through the application of the asthma module of the International Study of Asthma and Allergies in Childhood, taking into account the totality of the data rather than responses to individual questions.

Keywords: Asthma/diagnosis; Asthma/epidemiology; International cooperation; Questionnaires