What Is Forced Expiratory Volume in One Second (FEV1) Testing?

How the amount of air you can exhale is used in pulmonary testing

Elderly patient using an inhalation mask
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Forced expiratory volume in one second (FEV1) is a measurement of your ability to expel air from your lungs. More specifically, and as its name suggests, it is the amount that is exhaled in the first second of purposefully trying to breathe out as much air as possible.

Measured via spirometry, your FEV1 value can be used to help diagnose and monitor lung diseases.

Purpose of Test

FEV1 testing is used when you have signs of impaired lung function.

Many pulmonary diseases affect your lungs in a way that slows down the rate at which you exhale. However, some lung diseases have a greater impact on your exhalation rate than others, making FEV1 a useful measurement for differentiating between the various types of lung disease.

While results can't diagnose a pulmonary condition, they can be paired with those of other tests to help reach such a conclusion.

Your doctor may also perform repeat FEV1 testing to gauge if and how a pulmonary condition such as chronic obstructive pulmonary disease (COPD) is progressing.

Indications for an FEV1 test include:

  • Symptoms: You might need to have your FEV1 measured if you have respiratory symptoms such as shortness of breath or wheezing.
  • Physical examination findings: Signs such as tachypnea (rapid breathing) or a low oxygen level may be indications for an FEV1 measure.
  • Disease monitoring: When you are diagnosed with a pulmonary condition, such as pulmonary sarcoidosis or COPD, your medical team may periodically measure your FEV1 to determine whether your condition is improving or worsening over time.
  • Assessing the effectiveness of medication: If you are taking medication for a pulmonary condition, your doctor might obtain follow-up FEV1 measures to help determine whether or not your medication is helping your lung function.

Associated Tests

FEV1 is one of the pulmonary function tests (PFTs) done to evaluate lung function.

One of the distinguishing features of FEV1 is that it is time-dependent. A similar measurement—forced vital capacity (FVC), the volume of air that you can exhale after taking in a full exhalation—is not.

FEV1 and FVC values are often obtained in the same session, and the FEV1/FVC ratio is often used to help distinguish between obstructive and restrictive lung diseases (which cause similar symptoms, but have different causes).

Risks and Contraindications

Spirometry, for FEV1 or other measurements, requires your cooperation and effort, and it is considered safe. You should have your FEV1 measured under medical supervision to ensure an accurate measurement.

Using another person's at-home spirometer (the device used to measure FEV1) is not advised, as it can exposure you to contagious organisms that may lead to infection.

Before the Test

Prior to having your FEV1 measured, your medical team will provide you with instructions regarding your medications. What you take can change your results, and your doctor may want to assess your respiratory function with or without it.

Be sure to talk to your doctor about any new health issues before your test is scheduled. For example, an infection can affect your results, and your team may want to re-schedule your test for after your infection has cleared.

It is also important that you let your doctor know if you smoke (and how much), as smoking affects your expiratory abilities.

Timing

An FEV1 test should take about 10 minutes. However, you will likely also have other PFTs, so it is a good idea to check about the anticipated duration of the complete set of tests you'll be getting in advance.

Additional testing, such as imaging, can result in your appointment lasting a few hours.

Location

You will have your FEV1 test done either at your doctor's office or a pulmonary function testing laboratory.

What to Wear

Be sure to wear loose comfortable clothing. When you have this test, it is important that you are able to breathe without any restrictions, such as a tight belt or collar.

Food and Drink

You can eat and drink as usual prior to having your FEV1 test.

Cost and Health Insurance

The cost of your FEV1 test may be covered by health insurance. However, this is not always the case, and you may be required to pay a co-pay or the whole cost of the test.

If you are paying for your FEV1 out of pocket, the cost can range from $40 to $80. If you are having additional PFTs or other tests in addition to your FEV1, the cost will be higher.

What to Bring

Be sure to have the order for your test with you when you go to have your FEV1 measured, if it hasn't been filed electronically. You should also bring a form of identification, your insurance card, and a method of payment.

In addition to also bringing a list of all the medications you take, bring any prescribed for your pulmonary condition with you as well (most importantly, your inhalers). Your test may include an FEV1 measurement without your inhaler, followed by an FEV1 measurement with your inhaler.

During the Test

When you go in to have your FEV1 test, you may meet with a doctor, a nurse, and/or a pulmonary technician.

Pre-Test

You will be asked to sit in a chair and begin by breathing comfortably. You will then be given specific instructions regarding how to perform the test, such as when to inhale and exhale, and how to ensure maximal effort.

A clip will then be placed over your nose.

Throughout the Test

A spirometer has a tube that you must seal your lips tightly over. Once you do, you will be instructed to inhale as deeply as possible and exhale as forcefully as you can.

Your exhaled air volume will be measured at one second. Your team may also measure your total air volume exhaled. These readings will be instantly displayed.

The procedure is repeated at least three times to obtain a consistent and average value.

After your measurements are taken, you may have the whole test repeated after you use a bronchodilator—a type of medication that opens your airways.

The difference in your lung function with and without a bronchodilator helps identify whether this treatment has a substantial effect on your respiratory function.

You may also have other PFTs done, including FCV, vital capacity (VC), peak expiratory flow rate, and forced expiratory flow rate.

Post-Test

You should feel fine after your FEV1 test, and you will be able to continue with your usual daily activities.

Rarely, the test can make you feel a bit out of breath due to the effort exerted. If you feel any discomfort, tiredness, dizziness, or shortness of breath, be sure to tell your medical team before you go home.

Interpreting Results

Your FEV1 is compared against predicted values, which are the average readings that would be expected in a healthy person of similar age, gender, body size, and ethnicity.

Diminished FEV1 values generally indicate that you have lung obstruction, which is a blockage that prevents air from getting out of your lungs as you exhale.

The percentage of FEV1 reduction can be used as a guideline to assess the severity of your disease.

FEV1 (% of standard value) Indication
80% to 100% Normal
60% to 79% Mild pulmonary obstruction
40% to 59% Moderate pulmonary obstruction
40% or less Severe pulmonary obstruction

FEV1/FVC Ratio

While FVC is reduced to about the same degree in obstructive and restrictive lung disease, FEV1 is more severely diminished in obstructive lung disease.

A normal FEV1/FVC ratio is 70% to 80% or higher in adults, and 85% or higher in children.

  • Reduced FEV1 with an FEV1/FVC ratio in the normal range is consistent with restrictive lung diseases, such as pneumonia, sarcoidosis, and pulmonary fibrosis.
  • An FEV1/FVC ratio below 70 to 70 percent is more consistent with obstructive lung diseases like COPD, asthma, and cystic fibrosis.

If your FEV1 is reduced and the value improves by 12% after re-testing with use of an inhaled bronchodilator, your condition is likely to improve with such treatment.

Follow-Up

Depending on your test results, your medical team may also obtain additional testing to assess a pulmonary condition. Additional diagnostic tests can include chest imaging studies, such as chest X-ray or chest computerized tomography (CT).

You may also have other pulmonary tests, such as an arterial oxygen level, or functional residual capacity (FRC).

If you are diagnosed with pulmonary disease, you will need treatment. And you will likely need to have your FEV1 and FEV1/FVC repeated at regular intervals (once a year, for example) to assess your condition and your response to treatment.

A Word From Verywell

FEV1 and other PFTs can play an important role in the management of pulmonary diseases. It's important to note, however, that your symptoms are more important than your numbers. Even if your tests are encouraging, be sure to communicate any changes in how you feel to your doctor in detail.

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