Objective: To develop and validate a Portuguese-language version of the Asthma Control Test (ACT) for use in Brazil. Methods: The study comprised 290 asthma outpatients over 12 years of age. The patients completed the ACT questionnaire and had an appointment with a pulmonologist in order to assess asthma control in two visits. In the first visit, the patients also underwent spirometry. The second visit took place at least four weeks later. Results: We found that a cut-off score of 18 points-to differentiate between subjects with controlled asthma and those with uncontrolled asthma-had a sensitivity of 93%, a specificity of 74%, a negative predictive value of 86% and a positive predictive value of 85%. The positive and negative likelihood ratios were 3.58 and 0.09, respectively. The questionnaire has an outstanding capacity to differentiate uncontrolled asthma from controlled asthma, with an area under the ROC curve of 0.904. The patients whose symptoms remained stable between the two visits had similar scores, demonstrating good test-retest reproducibility, with an intraclass correlation coefficient of 0.93. The patients whose symptoms improved in the second visit had significantly higher scores, demonstrating good responsiveness of the questionnaire in the identification of changes in disease control. Conclusions: The Portuguese-language version of the ACT showed good test-retest reproducibility and was capable of discriminating the levels of asthma control and detecting changes in asthma control in a population of patients with a low level of education and low family income at a public health facility in Brazil.

Keywords: Asthma; Questionnaires; Validation studies; Signs and symptoms.