ABSTRACT
Asthma is one of the most common chronic diseases with an increasing prevalence. The cough variant of asthma [CVA] is a latent form of the disease. The aim of this study is to compare the decreasing rates of FEV1 and PEF during the methacholine challenge test. In this study, we tested a total of 120 patients [14-65 years old], whom were referred to the respiratory clinic with complaints of chronic cough, using normal chest and sinus x-ray and spirometry. Also other causes of chronic cough were ruled out. Spirometry and Peak Flowmetry were done during the methacholine challenge test, then FEV1 and PEF were recorded. From 120 patients, 47 patients [39.2%] were male and 73 [60.8%] were female. Thirty three [27.5%] patients showed a >/= 20% decrease in FEV1, while 35 patients [29.2%] had a >/= 20% decrease in PEFp. Decreasing values of FEV1 and PEFp with r=0.49 and P-value<0.000l were significant. Normalization for age, sex, and occupation shows that these factors have no effects on the decrease observed for FEV1 and PEFp. Based on the correlation ratio for PEFp in comparison with spirometry's FEV1, we suggest using peak flowmetry instead of spirometry for diagnosing CVA. According on the ROC curve, we recommend a >/= 15.5% decrease in the level of PEFp with 79% sensitivity and 69% specificity