What Does Spirometry Diagnose?

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

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What type of test is a spirometry and why is an important pulmonary function test What role does it play in the diagnosis and management of conditions such as lung cancer and COPD?

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. Overall, it tells you how much air you are moving through your lungs, as well as how fast this occurs.

If you have had a peak flow done in the office, this test is similar but more accurate.

It may seem difficult to understand the numbers and meaning of your tests, but take a moment to learn about your spirometry. Once you understand the numbers you will be in the best position possible to manage any lung condition you may have.

Let's talk about why this test is one, what conditions it can distinguish, and then go into what values are abnormal.

Reasons for Doing Spirometry

Spirometry plays an important role in both diagnosing and management many lung conditions. It can be used to distinguish conditions that may appear similar based on symptoms alone. It is also very helpful as an objective measure of how a lung disease is progressing and how it is responding to treatment. 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.
  • Determine the severity of a lung disease.
  • Determining lung function before lung surgery - Spirometry is an important test prior to surgery for many reasons. It gives surgeons an idea of how well a person with lung disease may tolerate surgery from a respiratory standpoint, as well as how a person may respond to having a portion of or a whole lung removed.
  • While not used routinely for this, a 2017 study found that spirometry was a very useful tool for predicting the presence of lung cancer in people exposed to asbestos. Enough so that researchers have recommended that spirometry should be offered to all workers who have had asbestos exposure and repeated every three years.

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.

How is a Spirometry Test Done?

Spirometry is usually done in your doctor's office. During a spirometry, you will be seated in a chair and asked to breathe normally for awhile. You will then be given a mouthpiece to place your mouth over which is connected to the machine called a spirometer. (A clip may be placed over your nose to make sure your entire breath enters and leaves through your mouth.) Then you will be asked to take in a very deep breath and then blow out as forcefully as possible. Your doctor or respiratory therapist may have you repeat the test several times to make sure she gets an accurate reading. If your pattern shows obstruction see below) your doctor may have you use a bronchodilator (such as an inhaler) and compare your results both with and without the bronchodilator. Altogether, the test takes about 15 minutes, plus or minus time for repeat measurements. 

What Does the Test Measure? You 

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

The ratio of FEV1 to FVC will also be calculated.

Flow Pattern

Results of a spirometry can be normal or abnormal. If they are abnormal they appear in one of two patterns:

  • An 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. Since your FEV1, in this case, is less than what would be expected, the ratio of FEV1/FVC is lower than average.
  • A 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. In other words, the results are rarely used alone. 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.

Learn more about the difference between obstructive and restrictive lung diseases.

Obstructive Lung Diseases - Examples include:

  • Asthma
  • COPD (emphysema, chronic bronchitis, and bronchiectasis)

Restrictive Lung Diseases - Examples include:

  • Pulmonary fibrosis
  • Post-surgical (after a lumpectomy or pneumonectomy)
  • Obesity
  • Scoliosis

What Other Tests May be Needed?

Sometimes a spirometry alone is unable to determine if you have an obstructive or restrictive lung disease or some of both. For example, in the combination above a person could have both an obstructive lung disease (asthma) and a restrictive lung disease (such as pulmonary fibrosis)

A test that is sometimes used to help clarify this is a lung plethysmography.

Interpreting Your Spirometry Results

It may seem overwhelming when you look at your readings, but by breaking it down into a few steps as physicians do, you will be able to read and understand what is normal and what your results mean for you.

As a first step, just look at the numbers of your FVC and FEV1 and compare them with the results which were predicted based on the calculation using your height and weight. If the numbers are 80 percent or higher of predicted, the result in usually normal (note - there are always some exceptions so it's important to talk to your doctor.

If either your FVC or FEV1 are abnormal (less than 80 percent of predicted), further steps are needed to understand the results.

If either your FVC or FEV1 are abnormal, look at the results of your ratio of FEV1 to FVC. This may be printed as a fraction of FEV1 over FVC. If this number is over 70 percent it could be that you have a restrictive lung disease. If this number is less than 70 percent, you may have an obstructive lung disease.

Once again, it's important to note that there are exceptions, and other tests may be needed. Yet looking at your numbers up to this point will help you better understand what is occuring when you doctor discusses the next steps to take.

Severity of Disease Based on Spirometry Results

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.)

  • An FEV1 over 80 percent is considered normal.
  • An FEV1 of 60 to 79 percent characterizes mild obstruction
  • An FEV1 of 40 to 59 percent after a bronchodi as moderate.
  • An FEV1 of less than 40 percent characterizes Cas severe.

Measurements may be looked at both with and without a bronchodilator

If you have COPD, this measurement will be used along with other information to determine the "GOLD" grading system stage of your disease.

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.)

Bottom Line on Spirometry

Spirometry is a very useful and common test used to distinguish between lung diseases and to determine the severity - whether a disease is responding to treatment or progressing. At times, other pulmonary function tests will be used along with spirometry to further understand a disease. If you have had a spirometry, take a moment to have your doctor explain your numbers, as well as any change in your numbers over time. Being your own advocate and learning about your condition puts you in the best position to make sure you are getting the best treatment possible and doing all you need to do to have the best quality of life with your condition.

Also Known As: pulmonary function test

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