What spirometry (pulmonary function test) findings indicate asthma?

From the Guidelines

Asthma is indicated by spirometry findings of a low FEV1/FVC ratio, which is typically less than 80% of the predicted value, and bronchodilator responsiveness, defined as an increase in FEV1 of 12% or more and 200 ml or more after administration of a bronchodilator 1.

Key Spirometry Parameters

• FEV1 (Forced Expiratory Volume in 1 second): a measure of the volume of air that can be exhaled in one second, which is reduced in asthma
• FVC (Forced Vital Capacity): a measure of the total volume of air that can be exhaled, which may be normal or reduced in asthma
• FEV1/FVC ratio: a measure of the proportion of air that can be exhaled in one second, which is typically reduced in asthma
• Bronchodilator responsiveness: an increase in FEV1 after administration of a bronchodilator, which indicates reversible airway obstruction

Interpretation of Spirometry Results

Spirometry results should be interpreted in the context of the patient's symptoms and medical history, as a single abnormal test result is not sufficient to diagnose asthma 1.

Clinical Practice Guidelines

The American Thoracic Society/European Respiratory Society statement recommends that spirometry be measured at the baseline examination of most asthma clinical trials, and that FEV1 should be included as a primary endpoint for studies of bronchodilator therapy 1.

Additional Diagnostic Tools

Other diagnostic tools, such as exhaled nitric oxide fraction (FeNO) measurement, may be used to support a diagnosis of asthma in individuals with uncertain diagnosis, but should not be used alone to diagnose asthma 1.

From the Research

Spirometry Findings in Asthma

The following spirometry findings indicate asthma:

• Forced Expiratory Volume in one second (FEV1) is reduced, indicating airway obstruction 2, 3, 4
• FEV1/FVC ratio is decreased, indicating airway obstruction 2, 3, 4
• Post-bronchodilator FEV1 measures the best lung function that can be achieved by bronchodilator therapy on the day of the visit 2
• Airway responsiveness (bronchial challenge) measures the degree to which an individual withstands nonspecific stimuli that trigger asthmatic attacks 2
• Peak Expiratory Flow Rate (PEFR) is reduced, indicating airway obstruction 3
• Maximal Voluntary Ventilation (MVV) is reduced, indicating airway obstruction 3

Spirometry Parameters

The following spirometry parameters are used to assess asthma:

• Forced Vital Capacity (FVC) 3, 4
• FEV1 2, 3, 4
• FEV1/FVC ratio 2, 3, 4
• PEFR 3
• MVV 3

Asthma Diagnosis and Severity

Spirometry findings can help diagnose and assess the severity of asthma:

• A positive acute response to bronchodilator helps to confirm the diagnosis of asthma 2
• The degree of bronchodilator reversibility from visit-to-visit is not a useful index of asthma outcome 2
• Spirometry can help assess the severity of airway obstruction and monitor the effectiveness of treatment 2, 3, 4