Validity of Spirometry for Diagnosis of Cough Variant Asthma

  Background Cough variant asthma (CVA) is a chronic or recurrent cough without wheezing accompanied by bronchial hyper-responsiveness and eosinophilic inflammation of the airways. This study aimed to evaluate the validity of spirometry in the diagnosis of CVA, as well as determining the specificity and sensitivity of spirometry parameters in CVA. Materials and Methods This descriptive observational study was conducted from March 2015 to February 2016. The subjects were 73 patients 5 to 15 years of age who referred to the pulmonology clinics of Tabriz Pediatric Center, Tabriz city, Iran. The patients were divided into two groups of classic asthma (n=37), and CVA (n=36). Basic spirometry parameters such as FEV1/FVC and FEF25-75% were measured and the spirometry findings of each individual were measured based on European Respiratory Society (ERS) criteria. After intervention (β2 (beta2) adrenergic receptor agonists as bronchodilator test), in two groups, spirometry was again performed. The FEV1/FVC and FEF 25-75% parameters were examined for intervention. Data analysis was performed using SPSS (version 16.0).   Results Cut-off points for the diagnosis of CVA and classic asthma were obtained using FEV1/FVC and FEF 25-75% spirometry. The cut-off point for FEV1/FVC for the diagnosis of CVA was calculated to be 80%. When the FEV1/FVC ratio was higher than 80%, diagnosis of CVA was possible with a specificity of 94.59%, and sensitivity of 66.67%. These findings suggest a specificity and sensitivity of 94.59%, and 66.67%, respectively, for the diagnosis of classic asthma (with an FEV1/FVC ratio of below 80%). Analysis showed a positive predictive value of 100% for CVA at FEF 25-75% with a negative predictive value of 55.4%. Conclusion Spirometry can be a sensitive method for the diagnosis of CVA at a FEF 25-75% below 65%; however, it lacks the specificity for accurate diagnosis of CVA.