The Clinical Role of Changes of Maximum Expiratory Flow at 25% and 50% of Vital Capacity before and after Bronchodilator Reversibility Test in Diagnosing Asthma.

Changes of maximum expiratory flow at 25% and 50% of vital capacity (MEF ₂₅ and MEF ₅₀ , respectively), and predominant parameters indicating small airways function in asthmatics before and after bronchodilator (BD) reversibility test have been less interpreted. Our study aimed to investigate the clinical role of changes of MEF ₂₅ and MEF ₅₀ before and after BD reversibility test in diagnosing asthma. Forced expiratory volume in the first second (FEV ₁ ), MEF ₂₅ , and MEF ₅₀ were measured before and after BD reversibility test in 207 asthmatic patients using standard process. Forty healthy individuals were enrolled as controls. Receiver operating characteristic (ROC) curve was used to assess the diagnostic accuracy of reversibility of MEF ₂₅ and MEF ₅₀ before and after BD reversibility test (ΔMEF ₂₅ % and ΔMEF ₅₀ %, respectively) in diagnosing asthma. Among these functional criteria, ΔMEF ₂₅ % and ΔMEF ₅₀ % ≥ 25% performed the best diagnostic performance. The sensitivity, specificity, and accuracy of ΔMEF ₂₅ % ≥ 25% as an objective diagnostic test for asthma were 63.29%, 87.50%, and 67.21%, and of ΔMEF ₅₀ % ≥ 25% were 79.23%, 85.00%, and 80.16%, respectively. The area under the ROC curve of the indicators was 0.8203 and 0.9104, respectively. By contrast, an increase in FEV ₁ ≥ 12% and 200 mL demonstrated a sensitivity of 62.32%, specificity of 82.50%, and accuracy of 65.59% in diagnosing asthma. The changes of MEF ₂₅ and MEF ₅₀ before and after BD reversibility test may be of additional value in the clinical diagnosis of asthma, with cutoff values of 25% being the most.