What is Spirometry and What Does it Diagnose?

Reasons for a Spirometry, Diagnosis, and Role in Lung Cancer

diagram of man doing a spirometry test holding spirometer to his mouth
What is spirometry and when is it used?. A.D.A.M. Medical Encyclopedia

Definition: Spirometry

Spirometry is a type of pulmonary function test that measures the amount of air taken in (volume) and exhaled as a function of time.

During a spirometry test, a patient places their mouth over the mouthpiece of the spirometer, takes a deep breath in, and then blows out as forcefully as possible.

Reasons for Doing Spirometry

Spirometry may be ordered to:

  • Diagnose lung diseases
  • Measure respond to treatment - To see if a treatment such as a medication is helping a lung disease improve, or at least stabilizing that disease.
  • Determine progression of lung diseases - To see if they are getting worse.
  • Determining lung function before lung surgery (see next)

Spirometry in People with Lung Cancer

Spirometry may be done for people with lung cancer to evaluate and observe the response to treatment of respiratory symptoms. It may also be done to determine if lung surgery is recommended - in other words, to see if there is enough lung function so that lung cancer surgery would be tolerated.

What Does the Test Measure?

Spirometry gives health care professionals two important numbers that may indicate problems with lung function. These are:

Flow Pattern

Results of a spirometry can be normal or abnormal.

 If they are abnormal they appear in one of 2 patterns:

  • Obstructive pattern -  When the airways are narrowed (obstructed), the amount of air you can blow out quickly in 1 second (FEV1) is less than what would be expected based on your age, height,and weight.,and the ratio of FEV/FVC is lower than average.
  • Restrictive pattern - Restriction may include scarring in the lungs or deformities leading to a decreased ability of the lungs to function, rather than obstruction of the airways. For this reason, FVC is decreased but the ratio of FEV1/FVC is normal (both are decreased proportionally.)

Numbers in Spirometry

When spirometry is done, numbers are obtained for the measurements above. These numbers may be measured both without medications and again after using a bronchodilator.

  • Obstructive pattern - FEV1 less than 80 percent of predicted, and FEV1/FVC equal to 0.7 or less.
  • Restrictive pattern 

Conditions Diagnosed with Spirometry

Spirometry is a helpful test, but is used in combination with other findings on history, physical, and imaging tests to make a diagnosis. Spirometry may be used to help diagnose:

Patterns and Lung Disease

The pattern seen on spirometry may be used to separate out different form of lung disease, for example:

  • Obstructive pattern - An obstructive pattern will be seen in lung conditions affecting the airways such as COPD and asthma.
  • Restrictive pattern - A restrictive pattern will be seen in conditions in which there is direct lung damage and scarring such as pulmonary fibrosis.
  • Combination pattern - If people have more than one lung disease—such as cystic fibrosis and asthma—a combination pattern may be seen on spirometry.

Severity of Disease

In addition to separating out obstructive vs restrictive lung disease patterns, spirometry may give an indication of how severe a disease is. With COPD these levels refer to what the numbers are after someone has used a bronchodilator. In other words, they refer to how much of the obstruction is not reversible (and therefore, likely permanent.)

  • COPD would be referred to as mild for an FEV1 of 80 percent
  • An FEV1 of 50 to 79 percent after a bronchodilator characterizes COPD as moderate.
  • An FEV1 of 30 to 40 percent after a bronchodilator characterizes COPD as severe.

Risks of the Procedure

Spirometry is a very safe procedure, but some people may become lightheaded with the deep breaths taken during the test. It's not recommended that people have the test done if they've had a recent heart attack or stroke, or with conditions such as a collapsed lung (pneumothorax.)

Also Known As: pulmonary function test


National Library of Medicine. Pulmonary function tests. Updated 12/03/13. https://www.nlm.nih.gov/medlineplus/ency/article/003853.htm

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