Post-Bronchodilator FEV1/FVC Interpretation

Key Interpretation Principles

• The American Thoracic Society recommends that the FEV1/FVC ratio should be reported as a decimal fraction and compared to the absolute threshold of 0.70 or the lower limit of normal (LLN), not to a predicted value 1
• The FEV1/FVC ratio is an inherently relative measure that doesn't require normalization to predicted values, according to the American Thoracic Society 1

Clinical Application

• The Global Initiative for Chronic Obstructive Lung Disease (GOLD) guideline criterion for confirming COPD diagnosis is a post-bronchodilator FEV1/FVC ratio < 0.70, which can be compared to either the fixed threshold of 0.70 or the LLN (typically a z-score of -1.64) 1
• Disease severity classification is based on the post-bronchodilator FEV1 percent predicted, NOT the FEV1/FVC ratio, as stated by the European Respiratory Society 2

Bronchodilator Response Assessment

• When assessing bronchodilator response, the change in FEV1 and FVC (not the ratio) should be evaluated using both percent change from baseline (>12%) and absolute change (>200 mL), according to the European Respiratory Society 3, 4, 5
• The FEV1/FVC ratio can be misleading for assessing bronchodilator response if expiratory time changes, as noted by the European Respiratory Society 2, 4