Assessing two spirometric criteria of pre-bronchodilator and post-bronchodilator FEV1/FVC ratio in detecting air flow obstruction

Objectives: To assess the Pre-bronchodilator criteria and the Post-bronchodilator criteria of FEV1/FVC ratio in diagnosing Airflow obstruction. Methods: An observational study was conducted from 1988 to 2006 at the Aga Khan University Hospital. Patients referred to the pulmonary function test laboratory for spirometry with bronchodilator reversibility at the hospital during the above said period were enrolled. Forced spirometry was performed according to ATS guidelines. All patients who had pre-bronchodilator criteria of airflow obstruction were analyzed and compared with the post bronchodilator criteria. Results: A total of 4222 individuals underwent spirometry out of which 4072 individuals were studied.Using the pre bronchodilator criteria, 1375 (34%) patients had airflow obstruction. Applying the post bronchodilator criteria on the same patients, 1098 (27%) had evidence of airway obstruction. Out of these 1375 patients who had airflow obstruction by using pre-bronchodilator criteria, 277 (20%) patients had no airflow obstruction by using the post bronchodilator criteria. Out of these 277 patients, 52% had significant airways reversibility as evidenced by 12% increase in their FEV1 pre and post bronchodilator. Conclusion: Pre bronchodilator criteria for detection of airflow obstruction overestimate the diagnosis of airflow obstruction and by using post bronchodilator criteria for airway obstruction on spirometry, decreases this over diagnosis of the condition.