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 u sed to diagnose asthma in children. METHODS: Participants were childre n, predominantly aged 6 to 12 years, selected from three primary schoo l grades among 18 different schools in Montreal. Of 1111 participants, 989 successfully completed a six-minute free running test at school a nd returned a respiratory questionnaire. A total of 952 children had c omplete information that could be used for analysis. A history of whee zing in the past year in conjunction with a past diagnosis of asthma d efined current asthma by questionnaire. Exercise responsiveness was de fined as a greater than or equal to 10% fall in FEV1 after a six-minut e free run. As there is no perfectly accurate diagnostic test for asth ma, we analyzed the data using a previously published Bayesian method that allows for the estimation of test properties when no gold standar d test is available. RESULTS: Current asthma by questionnaire was foun d to have significantly higher specificity (94.9%, 95% credible interv al (CI): 93.2-96.5 versus 82.6%, 95% CI; 79.9-85.1) and positive predi ctive 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 sensitiv ity and negative predictive values, the estimates were higher for curr ent asthma (64.4%, 95% CI: 50.9-76.6 and 96.7%, 95% CI: 94.6-98.1, res pectively) 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 ident ifying subjects with asthma in community based studies.