Bayesian estimation of asthma prevalence, and comparison of exercise and questionnaire diagnostics in the absence of a gold standard.

PURPOSE To estimate the sensitivities, specificities, and predictive values of exercise challenge and questionnaire, when these tests are used to diagnose asthma in children. METHODS Participants were children, predominantly aged 6 to 12 years, selected from three primary school grades among 18 different schools in Montreal. Of 1111 participants, 989 successfully completed a six-minute free running test at school and returned a respiratory questionnaire. A total of 952 children had complete information that could be used for analysis. A history of wheezing in the past year in conjunction with a past diagnosis of asthma defined current asthma by questionnaire. Exercise responsiveness was defined as a > or = 10% fall in FEV1 after a six-minute free run. As there is no perfectly accurate diagnostic test for asthma, we analyzed the data using a previously published Bayesian method that allows for the estimation of test properties when no gold standard test is available. RESULTS Current asthma by questionnaire was found to have significantly higher specificity (94.9%, 95% credible interval (CI): 93.2-96.5 versus 82.6%, 95% CI: 79.9-85.1) and positive predictive value (53.8%, 95% CI: 41.0-66.7 versus 19.2%, 95% CI: 12.3-27.8) in comparison to exercise challenge. While there was no statistically significant difference between the two tests with respect to sensitivity and negative predictive values, the estimates were higher for current asthma (64.4%, 95% CI: 50.9-76.6 and 96.7%, 95% CI: 94.6-98.1, respectively) in comparison to exercise challenge (51.3%, 95% CI: 37.8-64.5 and 95.4%, 95% CI: 93.2-97.1, respectively). Agreement between the two diagnostic methods was poor and the combined use of the two tests did not significantly improve the likelihood of correctly identifying children with asthma. CONCLUSIONS Our findings support the view that exercise testing adds little to a well designed questionnaire in identifying subjects with asthma in community based studies.