Bronchodilation Test with Inhaled Salbutamol Versus Bronchial Methacholine Challenge to Make an Asthma Diagnosis: Do They Provide the Same Information?

BACKGROUND: Methacholine bronchial challenge and bronchodilation to salbutamol are key tests in clinical practice to make asthma diagnosis. OBJECTIVE: To assess the concordance between the 2 tests and to see whether they actually identify the same population of asthmatics. METHOD: We conducted a retrospective study using our asthma clinic database to see how methacholine bronchial challenge compared to bronchodilation to salbutamol in untreated patients with recurrent or chronic symptoms suspicious of asthma. We identified 194 untreated patients with baseline forced expiratory volume in 1 second (FEV(1)) ≥70% predicted who had both a bronchodilation test with salbutamol and a methacholine bronchial challenge 7 to 14 days apart. A positive bronchial challenge was a provocative concentration of methacholine causing a 20% fall in FEV(1) ≤16 mg/mL, whereas a positive bronchodilation test was a reversibility to 400 μg inhaled salbutamol ≥12% from baseline and 200 mL. RESULTS: Overall, asthma diagnosis was confirmed in 91% of cases leaving 9% of subjects with double negative tests. Isolated positive methacholine challenge was found in 71% of subjects, double positive tests in 17%, whereas isolated significant bronchodilation to salbutamol was rare (3%). There was no correlation between provocative concentration of methacholine causing a fall in FEV(1) of 20% (PC20M) and the magnitude of salbutamol reversibility (P = .10). Baseline FEV(1)/forced vital capacity ratio inversely correlated with reversibility to salbutamol (P < .001) but not with PC20M (P = .1). No difference was found between the groups regarding demographic and immunoinflammatory features, including the proportion of eosinophilic asthma. CONCLUSION: We conclude that methacholine challenge outperforms reversibility to salbutamol to diagnose asthma without selecting patients with distinct inflammatory profile. Baseline airway obstruction predicts magnitude of reversibility but not hyperresponsiveness.