How do I interpret spirometry figures, including Forced Expiratory Volume in one second (FEV1) and Forced Vital Capacity (FVC), to diagnose and treat Chronic Obstructive Pulmonary Disease (COPD) and asthma?

From the Guidelines

To interpret spirometry figures for diagnosing COPD and asthma, focus on the FEV1, FVC, and their ratio (FEV1/FVC), with a post-bronchodilator FEV1/FVC ratio below 0.70 indicating airflow obstruction in COPD, as recommended by the GOLD Science Committee in 2025 1. When interpreting spirometry results, consider the following key points:

• For COPD diagnosis, look for an FEV1/FVC ratio below 0.70 after bronchodilator use, which indicates airflow obstruction.
• The severity of COPD is then classified based on FEV1: mild (≥80% predicted), moderate (50-79%), severe (30-49%), or very severe (<30%).
• For asthma, look for an FEV1/FVC ratio below the lower limit of normal and FEV1 improvement of ≥12% and ≥200mL after bronchodilator administration, indicating reversible airflow obstruction. Some important considerations when interpreting spirometry results include:
• COPD typically shows persistent airflow limitation with minimal bronchodilator response, while asthma shows significant reversibility.
• The shape of the flow-volume loop is also informative - a scooped-out appearance in expiratory flow suggests obstructive disease.
• Serial spirometry measurements are valuable for monitoring disease progression and treatment response over time.
• The absolute values should always be interpreted in the context of predicted values based on the patient's age, height, sex, and ethnicity, as well as clinical presentation and exposure history. Treatment decisions for COPD and asthma should be based on the severity of the disease and the patient's response to treatment, with options including:
• Long-acting bronchodilators (like tiotropium 18mcg daily or salmeterol 50mcg twice daily) and inhaled corticosteroids (such as fluticasone 250-500mcg twice daily) for COPD.
• Stepwise approaches based on symptom control and lung function for asthma, ranging from as-needed short-acting beta-agonists to regular inhaled corticosteroids and add-on therapies like long-acting beta-agonists or biologics for severe disease. It is essential to note that the use of pre- or post-bronchodilator measurements in the diagnostic process is crucial, and the GOLD Science Committee recommends using post-bronchodilator values to confirm the diagnosis of COPD 1. Additionally, the threshold FEV1/FVC ratio that should be used to confirm an airflow limitation is uncertain, but a post-bronchodilator FEV1/FVC ratio of <0.7 has traditionally been the criterion for airflow limitation 1.

From the Research

Interpreting Spirometry Figures

To interpret spirometry figures, including Forced Expiratory Volume in one second (FEV1) and Forced Vital Capacity (FVC), for diagnosing and treating Chronic Obstructive Pulmonary Disease (COPD) and asthma, consider the following points:

• FEV1 measures the volume of air exhaled in the first second of a forced exhalation, while FVC measures the total volume of air exhaled during the entire forced exhalation 2.
• The ratio of FEV1 to FVC (FEV1/FVC) is used to diagnose obstructive and restrictive lung diseases. A lower ratio indicates an obstructive pattern, while a higher ratio indicates a restrictive pattern 3, 4.
• In COPD, the post-bronchodilator FEV1 is typically less than 80% of the predicted value, and the FEV1/FVC ratio is less than 70% 4.
• In asthma, the FEV1/FVC ratio may be normal or increased, and the response to bronchodilator therapy is often used to diagnose the condition 5.
• The change in FEV1 after bronchodilator therapy (ΔFEV1BDR) can be used as a diagnostic criterion for asthma, with increases of ≥12% and ≥200 mL from the baseline FEV1 commonly used as cut-off values 5.

Key Spirometry Parameters

Some key parameters to consider when interpreting spirometry figures include:

• FEV1: volume of air exhaled in the first second of a forced exhalation
• FVC: total volume of air exhaled during the entire forced exhalation
• FEV1/FVC: ratio of FEV1 to FVC, used to diagnose obstructive and restrictive lung diseases
• ΔFEV1BDR: change in FEV1 after bronchodilator therapy, used as a diagnostic criterion for asthma
• Peak Expiratory Flow Rate (PEFR): maximum flow rate achieved during a forced exhalation, often used to monitor asthma symptoms 6.

Diagnosing COPD and Asthma

When diagnosing COPD and asthma using spirometry, consider the following:

• COPD: post-bronchodilator FEV1 < 80% of predicted value, FEV1/FVC ratio < 70% 4
• Asthma: ΔFEV1BDR ≥ 12% and ≥ 200 mL from baseline FEV1, FEV1/FVC ratio may be normal or increased 5
• Mixed obstructive and restrictive pattern: may require additional diagnostic tests to distinguish between COPD and asthma 3.