Objective To explore the value of bronchial diastolic response (BDR) test in predicting the cough variant asthma (CVA) in patients with chronic cough or negative result of BDR test.

Methods A total of 140 patients with chronic cough and negative result of BDR test were selected and treated with inhaled corticosteroids (ICS) and long-acting β2-agonists for 4 weeks, and their lung functions were detected before and after treatment. Receiver operating characteristic (ROC) curve was used to evaluate the predictive values of the forced expiratory volume in the first second as a percentage of predicted value (FEV₁ %), exhaled nitric oxide (FeNO), forced expiratory flow at 25 % to 75 %(FEF_{25 % to 75 %})and forced expiratory flow rate in 25 % to 75 % (FEF %_{25 % to 75 %}) alone or their combined diagnosis.

Results After treatment, there were 98 cases diagnosed as negative for CVA and 42 cases diagnosed as positive for CVA. In combination of evaluation indexes, the top three combinations for CVA diagnosis were FEF %_{25 % to 75 %}+△FEV₁ %, FEF_{25 % to 75 %} +FeNO, and △FEV₁ +△FEV₁ %. Venn diagram of the combined prediction showed that there was an overlap in CVA positive diagnostic patients with FeNO ≥ 41.50×10^-9 mol/L, △FEV₁ % ≥ 5.90 %, and FEF %_{25 % to 75 %} ≤ 61.99 %.

Conclusion After treatment, patient's showing FeNO ≥ 41.50×10^-9 mol/L, △FEV₁ % ≥ 5.90 % and FEF %_{25 % to 75 %} ≤ 61.99 % can be used to predict CVA and the response to anti-asthma treatment.