How to read spirometer test results

Updated February 21, 2017

A spirometer is a device used by health professionals to measure abnormal lung function. It is also used to help determine how well a patient is responding to treatment for lung diseases such as asthma. Taking the test involves blowing quickly and hard into a tube attached to a meter. In just a few seconds, your doctor can measure how well you exhale.

Read the spriometer graph for forced vital capacity (FVC). When you blow hard and fast into the spirometer, forcing air out of your lungs, this is the maximum volume of air you can exhale. It is measured in liters.

Read the spirometer graph for forced expiratory volume in one second, also known as FEV1. When you blow hard and fast into the spirometer, this is the maximum volume of air you exhale in the first second. It is measured in liters per second.

Compare the values to healthy individuals in the same age, sex and height groups. Charts show thousands of readings taken from other patients and what normal values are for spirometer test results. These normal values are also called predicted values. If your results are abnormal, you could have asthma or another lung condition such as emphysema or COPD.

Interpret the numerical values from the spirometry. If your bronchial tubes are wide open, you will be able to exhale a large volume of air quickly. If they are narrowed due to asthma or another illness, the spirometer test results will show a lower number, meaning you are exhaling slower than the average person.

Determine whether the graph shows that your lungs are obstructed. If so, your doctor may ask you to take a quick acting asthma medicine such as albuterol, then repeat the test. If your second test results show that your lungs have opened up, they have responded to the asthma inhaler. You may have asthma.

Distinguish between different lung disorders by taking further tests. The spirometer cannot diagnose your illness, but it can tell you if your lungs are obstructed more than the norm. Discuss your health history with your doctor and have her examine you physically. This, combined with other pulmonary tests, will help her make an accurate diagnosis.


Form a tight seal around the mouthpiece when you blow into the spirometer. You might be given a nose clip to wear so that you exhale all of your air through your mouth. If you leak air from the tube, your results could be inaccurate or difficult to read.

Things You'll Need

  • Printouts from spirometer test
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