[Determining the most suitable spirometric parameters to differentiate chronic obstructive pulmonary disease [COPD] from asthma]

Chronic Obstructive Pulmonary Disease [COPD] and asthma are common diseases with difference in prognosis and treatment. It is believed that spirometry is the best modality for differentiating the two conditions; however, the data is heterogeneous. This study aims at determining the most suitable spirometric parameters in this regard. In this case control study, fifty patients [25 patients with asthma and 25 patients with COPD] in pulmonology ward of Dr.Faqi'hi Hospital of Shiraz in 2008 under the base spirometry and post bronchodilator were recruited and comparison between these two groups was done. The collected data was analyzed by the SPSS software using independent t-test, Man-Whitney, Chi-square and Fisher test. Frequency of male patients and the mean age were significantly higher in the COPD group. Increase of forced expiratory volume in one second [FEV1] after administration of bronchodilator was significantly higher in asthmatic patients with an optimal cut-off point of >/= 0.165 L [15% increase] yielded a sensitivity and specificity of 64% and 60%, respectively. Change of other parameters was not significantly different between the two groups. The best differentiating spirometric parameter was post-inhalation FEV1/predicted value with an optimal cut-off point of >/= 64.2, with relating sensitivity and specificity of 88%. According to our results and in concordance to other reports, changing of spirometric parameters after inhalation of a short-acting bronchodilator is not a reliable indicator of asthma or COPD. Post-inhalation FEV1/predicted value is the best parameter in this regard; however, the clinical suspicion should not be replaced by it