Understanding Spirometry

In order to diagnose and monitor asthma, your healthcare provider examines you. He or she listens to your chest and asks you to breathe. You are asked questions about your symptoms, triggers, and any family history of asthma or allergies. Special lung function tests may also be done. One of these is called a spirometry test.


Spirometry is an easy test that tells your healthcare provider how well your lungs are working. The spirometer measures the amount of air you exhale (breathe out) and how quickly you can exhale completely.

The National Heart, Lung, and Blood Institute recommends spirometry for people with asthma. Spirometry can help with the following:

What does it do?

When is it usually done?

It helps diagnose asthma.

It may be used when your healthcare provider is making a diagnosis.

It determines a person’s response to treatment.

It may be used after treatment is started and symptoms are more stable.

It can determine how severe asthma is.

It may be used during worsening or severe episodes.

It is used to monitor asthma.

It should be done at least every 1 to 2 years.

What does the spirometer measure?

It can take several different measures of your breath:

  • FVC (forced vital capacity). This is the total amount of air you exhale in a single, long breath.

  • FEV1 (forced expiratory volume in one second). This is the amount of air you exhale in the first second.

  • FEV1/FVC. This is the amount of air exhaled in the first second compared to the total amount of air exhaled. It’s given as a fraction or a percentage. In general, the higher the FEV1/FVC, the better. Normal values depend on your age.

  • PEF (peak expiratory flow). This is a measure of how fast you can exhale. It can be tested with a spirometer or a peak flow meter.

Talk with your health care provider about your spirometry results and what they mean. If you haven’t had spirometry in a year or two, ask your healthcare provider if you should have it done again.

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