Diagnostic value of post-bronchodilator pulmonary function testing to distinguish between stable, moderate to severe COPD and asthma

Daphne C Richter¹, James R Joubert¹, Haylene Nell¹, Mace M Schuurmans², Elvis M Irusen²

¹Tiervlei Trial Centre, Karl Bremer Hospital, Bellville, RSA; ²Respiratory Research Unit, Department of Internal Medicine, Faculty of Health Sciences, University of Stellenbosch, RSA

Objective: The GOLD guidelines suggest that the presence of a post-bronchodilator forced expiratory volume in one second (FEV₁) 80% of the predicted value in combination with a FEV₁/forced vital capacity (FVC) < 70% confirms the diagnosis of COPD. Limited data exist regarding the accuracy of these criteria to distinguish between COPD and asthma. The aim of this study therefore was to investigate the diagnostic value of post-bronchodilator lung function parameters in obstructive lung disease.

Methods: The pulmonary function tests of 43 (22 = COPD, 21 = asthma) patients with similar baseline characteristics were evaluated (baseline FEV₁ were 55.7% + 7.6%, and 59.3% + 8.4% predicted for COPD and asthma, respectively). Bronchodilator responsiveness (BDR) was calculated according to three recognized pulmonary function test criteria.

Results: The first criteria, post-bronchodilator FEV₁ < 80% of the predicted value in combination with a post-bronchodilator FEV₁/FVC ratio of <70%, had an accuracy of 70% to diagnose COPD. This combination was very sensitive (100%) in diagnosing COPD, but it was not specific (38%). The second BDR criteria, defined as an increase of <12% and 200 mL of initial FEV₁ and criterion number 3, an increase of <9% of predicted FEV₁, were less sensitive (55% and 59%, respectively), but more specific (81% and 76% respectively) to diagnose COPD. Our findings suggest that the current recommended spirometric indices are not optimal in differentiating between COPD and asthma.

Keywords: obstructive lung disease, diagnosis, post-bronchodilator pulmonary function test