From the Guidelines
Interpreting spirometry results involves understanding two key measurements: FEV1 (Forced Expiratory Volume in 1 second) and FVC (Forced Vital Capacity), with the FEV1/FVC ratio being the most important value to distinguish between obstructive and restrictive lung diseases, as stated in the most recent study 1.
Key Measurements
- FEV1 measures how much air you can forcefully exhale in one second
- FVC measures the total amount of air you can exhale after taking the deepest breath possible
Interpretation
- A normal FEV1/FVC ratio is typically above 70-75% 1
- In obstructive conditions like asthma or COPD, the FEV1 is reduced more than the FVC, resulting in a lower ratio (below 70%) 1
- In restrictive conditions like pulmonary fibrosis, both FEV1 and FVC are reduced proportionally, so the ratio often remains normal or even increases, but the overall volumes are lower than predicted based on your age, height, gender, and ethnicity 1
Severity Classification
- Severity is classified based on the percentage of predicted values: mild (>70%), moderate (60-69%), moderately severe (50-59%), severe (35-49%), and very severe (<35%) 1
Clinical Application
- These results help doctors determine appropriate treatment approaches, whether that involves bronchodilators for obstructive conditions or addressing the underlying cause of restrictive patterns 1
- The use of pre- and post-bronchodilator spirometry can help confirm the diagnosis of COPD and rule out other conditions 1
- The GOLD Science Committee recommends using pre-BD spirometry to rule out COPD and post-BD measurements to confirm the diagnosis, which can reduce clinical workload and limit COPD overdiagnosis 1
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Interpreting Spirometry Results
To interpret spirometry results, including Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC), in simple terms, consider the following points:
- FEV1 measures the amount of air exhaled in one second, while FVC measures the total amount of air exhaled [ 2 ].
- The FEV1/FVC ratio is used to diagnose obstructive lung disease, with a lower ratio indicating obstruction [ 2 ].
- A normal FEV1 does not necessarily indicate normal spirometry, as other tests such as FEF75, FEF25-75, and FEV1/FVC ratio may still show obstruction [ 3 ].
Key Factors to Consider
When interpreting spirometry results, consider the following factors:
- Age: The FEV1/FVC ratio decreases with age, and a fixed ratio of 70% may not be suitable for older adults [ 2 , 4 ].
- Ethnicity: The FEV1/FVC ratio may vary among different ethnic groups [ 5 ].
- Baseline lung function: The FEV1/FVC ratio at baseline is a strong influencing factor for the bronchodilation response [ 6 ].
Diagnosing Obstructive Lung Disease
To diagnose obstructive lung disease, consider the following:
- The American Thoracic Society recommends using the lower limit of normal (LLN) method to diagnose obstructive lung disease [ 2 ].
- A fixed FEV1/FVC ratio of 70% may misclassify patients with obstruction, especially at the extremes of age [ 2 ].
- The FEV1/FVC ratio is the most sensitive measure of early or mild airway obstruction in children with cystic fibrosis [ 3 ].