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Asthma & Spirometry- How Spirometry Is Used to Diagnose and Manage Asthma

What You Need to Know About Spirometry and Your Asthma


Updated May 31, 2014

Asthma & Spirometry- How Spirometry Is Used to Diagnose and Manage Asthma

Asthma and Spirometry

Photo © A.D.A.M.

What Is Spirometry?

Spirometry measures both how much and how fast air moves through your lungs. It's is much more reliable than peak flows and spirometers are required to meet certain standards from the American Thoracic Society. Depending on which specific tests are ordered, spirometry may take anywhere from 10 to 30 minutes.

From the patient perspective, spirometry is similar to a peak flow except:

  • It is preformed in a doctor's office
  • A machine, called a spirometer, collects data as you maximally inhale and forcefully exhale

Why Would My Asthma Provider Order Spirometry?

Spirometry may be useful to your asthma care provider in the following situations. Spirometry:

  • Cannot by itself diagnose asthma, but may help your asthma care provider make an asthma diagnosis
  • Aids in asthma management
  • Helps monitor the progression of your asthma over time

Spirometry results cannot be considered alone, but will help support or exclude your asthma diagnosis. After taking a thorough history and preforming a physical exam, spirometry may help establish an asthma diagnosis. Over time, spirometry measurements will indicate if your asthma is getting better or worse.

What Does Spirometry Measure?

Spirometry allows your asthma care provider to measure several aspects of your lung function that are important in determining both the severity and control of your asthma including:

How is Spirometry Preformed?

Spirometry is preformed with a device called a spirometer. It consists of a mouthpiece that is connected via tubing to a machine that records results and displays them graphically as you breathe in and forcefully exhale. In order to perform spirometry, a technician will ask you to:
  1. Apply a nose clip to prevent you from exhaling through the nose
  2. Have you breathe normally for a short time and then
  3. Inhale as deeply as possible
  4. Closes their mouth tightly around the tube and
  5. Exhale forcefully and completely through the mouth piece for as long as possible while maintaining a tight seal around the mouth piece

Spirometry will often be repeated three times to get your best and maximum effort. Your provider may also repeat the test after having you take a short acting bronchodilator like Albuterol.

What Do My Spirometry Results Mean?

Your FEV1 value expressed as a percentage of predicted can be used to classify the amount of obstruction occurring with your asthma:
  • FEV1 greater 80% of predicted= normal
  • FEV1 60% to 79% of predicted = Mild obstruction
  • FEV1 40% to 59% of predicted = Moderate obstruction
  • FEV1 less than 40% of predicted = Severe obstruction

Alternatively, if your doctor is unsure if you have asthma, an improvement in your FEV1 of 12% or more with a rescue medication helps your asthma care provider confirm a diagnosis.


National Heart, Lung, and Blood Institute. Accessed: January 1, 2009. Expert Panel Report 3 (EPR3): Guidelines for the Diagnosis and Management of Asthma

Clinical Pulmonary Function Testing, Exercise Testing, and Disability Evaluation. In Chest Medicine: Essentials Of Pulmonary And Critical Care Medicine. Editors: Ronald B. George, Richard W. Light, Richard A. Matthay, Michael A. Matthay. May 2005, 5th edition.

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