What Do Your COPD Spirometry Results Mean?
A spirometry test provides key data on lung function. Learn how these results are interpreted to assess airflow and determine the status of your lung health.
Chronic Obstructive Pulmonary Disease (COPD) is a widespread lung condition that affects how easily you can breathe. For those with symptoms like a persistent cough or shortness of breath, a doctor may recommend spirometry. This procedure assesses how well your lungs function by measuring airflow. Understanding these results provides insight into your lung health and a potential COPD diagnosis.
What Happens During a Spirometry Test?
A spirometry test measures the amount of air you can breathe out and how quickly you can do it. During the procedure, you will be seated, and a soft clip will be placed on your nose to prevent air from escaping. A technician will ask you to take the deepest breath you can and then seal your lips tightly around a mouthpiece.
You will then be instructed to blow all the air out of your lungs as hard and as fast as possible until they feel empty. To ensure the results are accurate, you may be asked to repeat this action a few times. Your doctor might advise you to avoid certain inhaled medications, smoking, or large meals to get a clear measurement.
Decoding Your Spirometry Numbers
Spirometry results are centered on a few key measurements. The first is Forced Vital Capacity (FVC), the total volume of air you can forcefully exhale after taking your deepest possible breath. FVC is a measure of your lung size, showing the maximum amount of air your lungs can hold and expel.
A second measurement is Forced Expiratory Volume in 1 second (FEV1). This value represents the amount of air you blew out during the first second of the FVC maneuver. If your airways are narrowed or obstructed, this value will be lower because it takes longer to get the air out.
From these two values, a ratio is calculated: the FEV1/FVC ratio. This figure, expressed as a percentage, compares the amount of air you exhaled in the first second to the total amount. This ratio is particularly useful for identifying airflow obstruction.
How Spirometry Confirms COPD
The numbers from your spirometry test are used to determine if the airflow limitation characteristic of COPD is present. The test is often performed before and after you inhale a bronchodilator medication, which helps to open up the airways. This helps determine if any airflow limitation is fixed or reversible.
A post-bronchodilator FEV1/FVC ratio of less than 0.70 (70%) is the spirometric requirement for a COPD diagnosis. This indicates a persistent airflow limitation that does not significantly improve with medication. A doctor will always interpret these results in combination with your symptoms, medical history, and other potential tests to make a definitive diagnosis.
Spirometry and COPD Stages
Once a COPD diagnosis is confirmed, spirometry results are used to classify the severity of the airflow obstruction. This staging is based on your FEV1 value compared to the predicted normal value for a person of your same age, height, sex, and ethnicity, expressed as “FEV1 % predicted.” The Global Initiative for Chronic Obstructive Lung Disease (GOLD) provides a widely used staging system.
The GOLD system has four stages of severity:
- GOLD 1 (Mild): An FEV1 that is 80% or more of the predicted value.
- GOLD 2 (Moderate): The FEV1 is between 50% and 79% of the predicted value.
- GOLD 3 (Severe): An FEV1 between 30% and 49% of the predicted value.
- GOLD 4 (Very Severe): The FEV1 is less than 30% of the predicted value.
These FEV1 percentages provide a standardized way for healthcare providers to understand the degree of lung function impairment and track the condition over time.