Acute bronchodilator response has limited value in differentiating bronchial asthma from COPD

Acute responsiveness to inhaled bronchodilators is often used to differentiate between bronchial asthma and chronic obstructive pulmonary disease (COPD). The response can be expressed in terms of a change in FEV1 and FVC in several ways-as absolute change, change as percent of baseline value, or as percent of predicted value with different thresholds for a positive test. A comprehensive evaluation of the diagnostic value of these different methods of expressing the acute bronchodilator response has not been carried out.

Response to inhaled salbutamol was measured by spirometry in 200 asthmatics and 154 patients with COPD. The sensitivity, specificity, and positive and negative predictive values of different methods of expressing responsiveness were calculated. Receiver operative characteristic curves were obtained.

None of the expressions of response gave a clear-cut separation between the two diseases. A DeltaFEV1>or=0.2 L gave the most satisfactory combination of sensitivity (73%) and specificity (80%) and the highest positive (82%) and negative predictive values (69%) for diagnosing asthma. These values were superior to those obtained for the ERS or the ATS criteria for reversibility (DeltaFEV1% predicted >or=9% and DeltaFEV1 of >or= than 12% and 0.2 L over the baseline, respectively), which had almost similar diagnostic characteristics. This was confirmed by the area under curve of the ROC plots. Expressions of response in terms of changes in FVC were unsatisfactory in separating the two diseases.

It was concluded that the test of acute bronchodilator responsiveness has limited diagnostic value in separating asthma and COPD.