Spirometry test for COPD: confirming diagnosis

COPD is defined by airflow obstruction that is irreversible or only partially reversible with bronchodilator treatment—and a spirometry test for COPD is the only objective way to confirm it. Spirometry measures how much air is inhaled and exhaled, and how quickly it moves through the lungs. Interpreting spirometry results is a matter of knowing what these values mean.

In this lesson from our COPD Essentials course you'll learn how to:

• Identify the key spirometry values — FEV₁, FVC, and the 
  FEV₁ / FVC ratio
• Apply the FEV₁ / FVC ratio to diagnose COPD
• Determine when pre- and post-bronchodilator spirometry is needed
• Recognize when the 0.7 diagnostic threshold may not apply

And you’ll see how a spirometry test for COPD is performed in a real pulmonary function lab demonstration.

Spirometry test for COPD diagnosis

[00:00]

Spirometry is required to make a formal diagnosis of COPD. It's the objective way of determining if airflow limitation is present and whether it's reversible. Airflow limitation that is irreversible or only partially reversible with bronchodilator treatment is the diagnostic feature of COPD.

What is spirometry?

[00:21]

But first, what is spirometry, and how do we use it for the diagnosis of COPD? A spirometer is a device that measures the volume of air that's inhaled and exhaled by the lungs. It can also detect the rate of flow measured in liters per second.

Key spirometry values for COPD testing

[00:39]

When you order a pulmonary function test for the diagnosis of COPD, or asthma, a technician will use the spirometer to obtain two important values. The first is a forced expiratory volume in one second, or FEV₁, which measures how much air the patient can exhale in one second. The second value is a forced vital capacity, or FVC, which refers to the entire amount of air the patient can forcibly exhale after taking a very deep breath. 

Performing a spirometry test for COPD

[01:13]

I went to the pulmonary function lab at my hospital and asked the respiratory therapist to put me through a standard spirometry evaluation for COPD. This is what I learned as she coached me through the process: 

“[We’re] just checking to see how well you can move your air in and out. So you're gonna pinch your nose and breathe normal on the mouthpiece. I'll tell you to take a big breath in nice and deep, and you're gonna blast your air out, pushing all that air in one breath. And then I'll tell you to bring your breath back in and you can disconnect.”

Interpreting spirometry results

[02:18]

The spirometry device generates a readout that lists FEV₁, FVC, and the ratio of the two. The definition for airflow obstruction for the diagnosis of COPD is a fixed FEV₁ to FVC ratio of less than 0.7.

When to skip post-bronchodilator spirometry

[02:34]

In the past, we would measure both a pre- and post-bronchodilator spirometry for all patients, but the guidelines have changed. If there is no airflow obstruction on the initial spirometry evaluation, there is no need to perform any post-bronchodilator spirometry. This adjustment significantly streamlines the process and reduces the need for patients to wait 30 minutes after bronchodilator administration. 

Confirming COPD with post-bronchodilator spirometry

[03:01]

But if the pre-bronchodilator spirometry results are consistent with airflow obstruction, then COPD is confirmed using post-bronchodilator measurements. Patients with a pre-FEV₁ / FVC ratio of less than 0.7 and a post-bronchodilator ratio greater than 0.7 may have asthma, or in the presence of COPD risk factors and symptoms, may be at an increased risk for future COPD and should be followed closely.

Limitations and considerations in COPD diagnosis

[03:32]

This is a good time to remind you that peak flow measurement is a useful screening tool for COPD, but it has poor specificity and can't reliably replace spirometry for diagnosis. But keep in mind, there are always exceptions. For example, using the 0.7 ratio as a diagnostic threshold for COPD in older patients may lead to overdiagnosis and underdiagnosis in younger patients. Remember that the diagnosis must be in the context of progressive COPD symptoms, as other lung diseases can also present with fixed airflow limitations.