What is a spirometry test?
Spirometry is a simple, non-invasive test that is used to diagnose COPD. When you take the test, you will be asked to blow all the air out of your lungs into a mouthpiece connected to a machine known as a spirometer.
The machine will calculate two numbers: the amount of air you blow out in the first second, and the amount of air you blow out in 6 seconds or more.
These numbers are represented as FEV1 and FVC (sometimes FEV6 is used). FEV1 stands for the Forced Expiratory Volume in the first second—the amount of air you exhaled in the first second of blowing. FVC stands for Forced Vital Capacity—the amount of air that you exhaled in one entire breath.
A spirometry test can also show your doctor how severe your COPD may or may not be. There are several stages of COPD. The extent of your COPD is classified into 4 different stages that are defined by your symptoms and the results of your Spirometry Test. The stages do not determine how long you can expect to live, or in many cases how drastically your symptoms are affecting your quality of life. The stages are designed to help your physician in prescribing your treatment protocol. In order to determine what stage you are in, your pulmonologist, based on your symptoms, may administer one or more pulmonary tests.
People with COPD have an FEV1/FEV6 (FVC) ratio less than 70%. The FEV1 percentage predicted indicates how severe the airways are obstructed (blocked or narrowed).
Less than 80% of predicted is considered moderate COPD, and less than 50% of predicted is severe. People with asthma will have a low FEV1/FEV6 ratio when they are having an attack, and then will return to normal or almost normal after using fast-acting medications.
Your doctor may order additional tests to see if your symptoms are caused by lung disorders other than COPD. One is Bronchodilator Reversibility Testing, which determines if your lung function improves significantly with medication.
Your doctor may also order a chest x-ray or a chest CT (high resolution computed tomography), which shows your lungs in much greater detail, to see if your symptoms are brought on by other problems instead of COPD.