Forced expiratory volume in the first second, or FEV1, is a spirometry test. It calculates how much air a person can force out of their lungs in 1 second. A lower score can indicate asthma.

FEV1 is a type of noninvasive pulmonary function test. These tests can show how well the lungs are working.

Specifically, FEV1 is a type of spirometry test. These tests measure the ability to inhale and exhale air. The FEV1 test calculates the amount of air a person can force out of their lungs in 1 second.

A doctor can use spirometry tests, such as FEV1, to help diagnose asthma, chronic obstructive pulmonary disease (COPD), and other conditions that affect lung function. Spirometry tests can also help monitor the progression of these lung conditions.

Asthma is a common lung condition that can cause occasional breathing problems. It is a chronic lung disease that occurs due to inflammation and muscle tightening around the airways. When this happens, it can make it harder to breathe.

A doctor can prescribe treatments to help a person manage their asthma. In severe cases, asthma can prevent oxygen from reaching the lungs, which can have serious health effects.

A pulmonologist monitoring a person's lung function during a spirometry test-2.Share on Pinterest
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Asthma is a chronic lung condition. It occurs when the inside walls of the airways swell due to inflammation. During an asthma attack, it becomes difficult for air to move in and out of the lungs.

To help diagnose asthma, a doctor often uses spirometry tests. These tests involve a person breathing in deeply and then breathing out forcefully into a tube. The tube connects to a machine, known as a spirometer, that shows the speed at which the person expels air from the lungs.

Forced expiratory volume (FEV) describes the volume of air a person can exhale during a forced breath. A doctor may measure how much air a person can breathe out for different durations.

For example, FEV1 refers to the maximum amount of air a person can forcibly expel during the first second after a deep inhalation.

With healthy lungs, a person can usually blow out most air from their lungs in 1 second. However, if a person has narrower airways due to asthma, it takes them longer to empty their lungs of air.

As such, a lower FEV1 value can indicate lung obstruction, which may be due to a lung condition such as asthma. The test can also help measure the severity of lung conditions.

In addition to living with a lung condition, a number of other factors can also influence FEV1. These include age, height, and sex. As such, a medical professional considers these factors when calculating a person’s FEV1 value.

Before the test, a doctor calculates a person’s predicted “normal” value. After performing the test, the doctor compares the test score with the prediction.

General guidelines suggest a score of 80% or higher of the predicted value suggests typical lung function. Some guidelines suggest 70% or more can indicate healthy airways.

The Centers for Disease Control and Prevention (CDC) provides a spirometry reference value calculator. This tool can help predict a FEV1 reading based on average values from healthy people of the same age, sex, height, and race.

However, it is important to note this value is not as accurate as one from a trained medical professional.

In addition to measuring FEV1, a doctor may also measure forced vital capacity (FVC). This refers to the maximum amount of air a person can forcibly exhale from the lungs after fully inhaling.

If a doctor has both the FEV1 and FVC values, they may calculate the FEV1/FVC ratio. This number represents the percentage of the lung size that a person can exhale in 1 second. If a person has a ratio lower than 70%, it suggests airflow limitation and obstruction.

If spirometry suggests a narrowing of the lungs, a person may need to do a bronchodilator reversibility test (BDR test). This is a spirometry test performed after taking bronchodilator medication. These drugs help relax and open the airways.

A BDR test can help determine whether a problem with the lungs is obstructive, restrictive, or a combination of the two.

Obstructive airway diseases refer to when a condition affects the ability to breathe out quickly due to a narrowing of the airways but lung capacity is normal. This includes conditions such as asthma and COPD.

Restrictive lung conditions describe a reduction in the amount of air a person can breathe in due to the lungs being unable to fully expand. This can occur with pulmonary fibrosis.

Read on to learn more about FEV1 and COPD.

In addition to helping diagnose asthma, FEV1 can also help determine the severity of the condition. Generally, the lower the FEV1 value, and the lower the FEV1/FVC ratio, the more severe the asthma.

However, while these values can help, a doctor’s assessment of symptoms is also important when gauging the severity of asthma.

A table from the American Lung Association provides the following information on asthma severity:

5 to 11 years• normal FEV1 between
• FEV1 over 80% predicted
• FEV1/FVC over 85%
• FEV1 equal to or over 80% predicted
• FEV1/FVC over 80%
• FEV1 60% to 80% predicted
• FEV1/FVC 75% to 80%
• FEV1 under 60%
• FEV1/FVC under 75%
12+ years
(normal FEV1/FVC:
•8 to 19 years: 85%
• 20 to 39 years: 80%
• 40 to 59 years: 75%
• 60 to 80 years: 70%)
• normal FEV1 between
• FEV1 over 80% predicted
• FEV1/FVC normal
• FEV1 equal to or over 80% predicted
• FEV1/FVC normal
• FEV1 60% to 80% predicted
• FEV1/FVC reduced 5%
• FEV1 under 60%
• FEV1/FVC reduced over 5%

A FEV1 test can help diagnose asthma. For example, following a BDR test, an increase in FEV1 by more than 200 milliliters or more than 10% of the pre-bronchodilator value indicates asthma.

A healthcare professional may use FEV1 in association with other tests to help diagnose asthma. Other tests a doctor may use to confirm an asthma diagnosis include:

  • challenge tests
  • allergy tests
  • blood tests

In addition to performing these tests, a doctor also takes into account a person’s symptoms as well as family and personal medical history.

FEV1 is the gold standard in clinical care and research for assessing asthma.

While health experts agree on the role of FEV1 in diagnosing asthma, there is less of a consensus on its role for monitoring and managing asthma.

According to the Global Initiative for Asthma, treatment to prevent and control asthma symptoms may include:

  • inhaled corticosteroid (ICS) inhaler
  • a reliever inhaler
  • managing modifiable risk factors, such as avoiding asthma triggers
  • non-pharmacological therapies and strategies, such as physical activity and quitting smoking, if applicable

Read on to learn more about:

Asthma is a common lung condition. It can cause breathing problems due to narrowing of the airways. A forced expiratory volume in the first second (FEV1) is a test that measures how much air a person can exhale in 1 second.

Narrowing of the airways can cause a person to take longer to empty their lungs of air. As such, a doctor can use the FEV1 test to help diagnose lung conditions such as asthma. An FEV1 test can also help indicate the severity of asthma.

However, while an FEV1 can help diagnose and gauge the severity of asthma, health experts are unsure whether it is useful for monitoring asthma.