Repeatability of histamine bronchial challenge and comparability with methacholine bronchial challenge in a population of Australian schoolchildren.

To measure the repeatability of the bronchial challenge test and the comparability of histamine and methacholine as provoking agents, we studied a population sample of children and conducted histamine bronchial challenge tests on each of 3 consecutive days followed by a methacholine bronchial challenge on the fourth day. Bronchial responsiveness was measured using the rapid inhalation method. A total of 393 children had satisfactory bronchial challenge data for all 4 days. The measurements derived from the dose-response curve were the PD20 FEV1, which was measured as the provoking dose causing a 20% fall in FEV1, and the dose-response slope (DRS), which was measured as the percentage fall in FEV1 at final dose/total dose administered. Children who had a PD20 FEV1 were categorized as having bronchial hyperresponsiveness (BHR). The percentage of children with BHR each day was between 7 and 11. One-third of the children with BHR reacted only to histamine or methacholine. The within-subject range for histamine PD20 FEV1 values compared with methacholine suggested that histamine and methacholine are not directly comparable bronchial challenge agents. The dose-response slope values, which could be obtained for all children, had slightly better repeatability than PD20 FEV1 values. Because DRS values obtain data for the entire sample, have good repeatability, and are equally repeatable in children with normal responsiveness or bronchial hyperresponsiveness, they should prove more useful than PD20 FEV1 values for measuring bronchial responsiveness in populations.