Forced Expiratory Volume at One Second (FEV1)

Forced expiratory volume at one second (FEV1) is a type of lung (pulmonary) function test. It measures how much air you can force out of your lungs and airways within one second after taking a big breath. If your lungs are healthy, more than 70% of the air leaves your lungs during the first second.

When is it performed?

Healthcare providers measure FEV1 during spirometry. Spirometry is a type of lung function test that providers use to:

• See how well your medications work
• Diagnose lung conditions like asthma and chronic obstructive pulmonary disease (COPD)
• See if a lung condition is getting worse

How does FEV1 work?

A spirometer measures your FEV1. A spirometer is a machine with a mouthpiece. You breathe into the mouthpiece. The spirometer calculates how much air you breathe in and out.

What to expect before the test

Before a healthcare provider determines your FEV1, they may ask you to:

• Avoid any intense physical activity for at least 30 minutes before the test
• Stop taking any breathing medications for a short time
• Wear loose, comfortable clothing that doesn’t squeeze or press against your chest, abdomen or neck

These steps help ensure accurate results.

You should also let your provider know if you’re sick or if you smoke. Illness or smoking can affect your breathing and test results.

What kind of healthcare provider does FEV1?

The following healthcare providers may perform FEV:

• Pulmonologist
• Respiratory therapist
• Primary care physician (PCP)
• Nurse

What to expect during the test

Your healthcare provider will first record your:

• Age
• Height
• Sex

This helps them compare your results to what’s typical for someone like you.

Then, they’ll place soft clips on your nose. The clips help you breathe in and out only through the mouthpiece.

When you’re ready, you’ll take a deep breath and blow air forcefully into the mouthpiece. You’ll do the test at least three times to get accurate results. You may have to repeat the tests after using a bronchodilator.

Can I measure my FEV1 at home?

No, you can’t measure FEV1 with a home device. But you can determine your peak flow. Your providers may sometimes suggest you check your peak flow between appointments.

How long does it take?

FEV1 testing usually takes only a few minutes. But it’s often just one part of pulmonary function testing. Your healthcare provider will give you a better idea of what to expect before the test.

What to expect after the test

If you had to stop taking any medications, you can start them again. You can also continue any of your usual activities, like exercise or any other physical activity.

What are the risks?

FEV1 is very safe, and it isn’t painful. But some people may feel tired, dizzy or lightheaded during testing. It’s OK to take breaks if you need to. Your provider will monitor you until you start to feel better.

How do you calculate FEV?

Healthcare providers usually measure and interpret your FEV1 together with your forced vital capacity (FVC). FVC is the total amount of air that you can forcefully and completely blow out after taking a deep breath. Healthcare providers calculate a percentage by dividing your FEV value by your measured FVC value.

What is a normal FEV1 value?

A normal FEV1/FVC ratio should be higher than what other people of the same age, height and sex can achieve. It’s typically above 70%.

Your results can help your provider determine if you have an obstructive lung disease or a restrictive lung disease.

Obstructive lung diseases include asthma, COPD and cystic fibrosis.

A restrictive lung disease is when a condition prevents you from fully inflating your lungs. Common causes include interstitial lung disease.

It’s important to have a specialist interpret your lung function testing results. You may have lower values than predicted, but not have a respiratory disease. It’s also possible to have a pulmonary condition that doesn’t affect your spirometry values. Your pulmonologist can tell the difference and make an accurate diagnosis.

When should I know the results of the test?

You should expect to get your test results within a few days. A specialist must first examine your results. They may also need to discuss your results with the provider who recommended FEV testing.

If the results are abnormal, what are the next steps?

If your FEV1 results are abnormal, your healthcare provider may recommend additional tests. These may include:

• Additional lung function testing
• Blood tests
• Chest X-rays
• Chest CT scans

Depending on your signs and symptoms, they may also recommend treatment like respiratory therapy, an inhaler or medications.

When should I call my doctor?

Reach out to your healthcare provider if you don’t hear your results from them within a few days. You may need to schedule regular visits to check on your condition.

Call your provider right away if you notice any changes in your breathing.