Baseline spirometry parameters as predictors of airway hyperreactivity in adults with suspected asthma

Background: Methacholine challenge tests (MCTs) are used to diagnose airway hyperresponsiveness (AHR) in patients with suspected asthma where previous diagnostic testing has been inconclusive. The test is time consuming and usually requires referral to specialized centers. Simple methods to predict AHR could help determine which patients should be referred to MCTs, thus avoiding unnecessary testing. Here we investigated the potential use of baseline spirometry variables as surrogate markers for AHR in adults with suspected asthma. Methods: Baseline spirometry and MCTs performed between 2013 and 2019 in a large tertiary center were retrospectively evaluated. Receiver-operating characteristic curves for the maximal expiratory flow-volume curve indices (angle β, FEV1, FVC, FEV1/FVC, FEF_50%, FEF_25–75%) were constructed to assess their overall accuracy in predicting AHR and optimal cutoff values were identified. Results: A total of 2983 tests were analyzed in adults aged 18–40 years. In total, 14% of all MCTs were positive (PC20 ≤ 16 mg/ml). All baseline spirometry parameters were significantly lower in the positive group (p < 0.001). FEF_50% showed the best overall accuracy (AUC = 0.688) and proved to be useful as a negative predictor when applying FEF_50% ≥ 110% as a cutoff level. Conclusions: This study highlights the role of FEF_50% in predicting AHR in patients with suspected asthma. A value of ≥ 110% for baseline FEF_50% could be used to exclude AHR and would lead to a substantial decrease in MCT referrals.