Immediate bronchodilator response in FEV₁ as a diagnostic criterion for adult asthma

Asthma is characterised by variable and reversible expiratory airflow limitations. Thus, it is logical to use the change in forced expiratory volume in 1 s (FEV₁) in response to a bronchodilator (ΔFEV₁BDR) as a diagnostic tool; increases of ≥12% and ≥200 mL from the baseline FEV₁ are commonly used values. We aimed to evaluate the historical development of diagnostic cut-off levels for the ΔFEV₁BDR for adults and the evidence behind these recommendations.We searched for studies from the reference lists of all the main statements, reports and guidelines concerning the interpretation of spirometry and diagnostics for asthma and conducted a literature search.A limited amount of evidence regarding the ΔFEV₁BDR in healthy populations was found, and even fewer patient studies were found. In healthy persons, the upper 95th percentile for the absolute ΔFEV₁BDR ranges between 240 mL and 320 mL, the relative ΔFEV₁BDR calculated from the initial FEV₁ ranges from 5.9% to 13.3% and the ΔFEV₁BDR calculated from the predicted FEV₁ ranges from 8.7% to 11.6%. However, the absolute and percentage ΔFEV₁BDR values calculated from the initial FEV₁ are dependent on age, sex, height and the degree of airway obstruction. Thus, the use of the ΔFEV₁BDR calculated from the predicted FEV₁ might be more appropriate.Not enough data exist to assess the sensitivity of any of the cut-off levels for the ΔFEV₁BDR to differentiate asthma patients from healthy subjects. Further studies in newly diagnosed asthma patients are needed.