What Is Forced Vital Capacity (FVC)?

What to expect when undergoing this test

Forced vital capacity (FVC) is the amount of air that can be forcibly exhaled from your lungs after taking the deepest breath possible. It's measured by spirometry, which is a common breathing test to check lung function.

This test may help distinguish obstructive and restrictive lung diseases. Obstructive diseases, such as asthma and chronic obstructive pulmonary disease (COPD), make it difficult to exhale all the air from your lungs. Restrictive lung diseases, such as pulmonary fibrosis and sarcoidosis, cause problems with inhaling air to fill your lungs.

FVC can also help healthcare providers assess the progression of lung disease and evaluate the effectiveness of treatment. An abnormal FVC value may be chronic, but sometimes the problem is reversible and the FVC can be corrected.

This article discusses the purpose of the FVC test. It covers what to expect during the test and how results are interpreted.

Lung function test
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Purpose of FVC

FVC is used to evaluate your lung function. It measures the effect that your lung disease has on your ability to inhale and exhale.

While FVC cannot identify which specific lung disease you have, the results can help narrow down potential diagnoses. It can be used—along with other studies—to help determine which lung disease you have.

Reasons you may need to have your FVC measured include:

Associated Tests

You may have other tests done when you go in to have your FVC measured. These include your vital capacity (VC) and forced expiratory volume over one second (FEV1).

FVC and VC record similar information. They both measure the amount of air you can exhale after maximally inhaling. But FVC refers to the amount of air you can exhale forcefully. VC records the maximum amount of air exhaled when breathing normally.

FEV1 differs in that it measures the amount of air you can exhale in one second.

Your FVC and other pulmonary function tests (PFTs) are used to establish the status of your lung function. They compare your measurements to standards based on your age, gender, race, height, and weight.

Recap

An FVC test measures the amount of air you can exhale forcefully after taking a deep breath. When used with other lung tests, it can help your doctor diagnose what kind of lung condition you have.

Risks and Contraindications

FVC requires your cooperation and effort, but it is safe. However, be sure to have medical supervision the first time you use a spirometer, the device used to measure your FVC. You could potentially use a spirometer the wrong way, exhausting yourself.

Afterward, you may be instructed on how to use it at home on your own. You should be sure the spirometer you use has been adequately cleaned before each use. That way you won't be exposed to anything that can cause an infection.

If a friend or family member uses home spirometry, don't use their device to measure your FVC or for other pulmonary function tests.

Before the Test

Before your FVC test, your healthcare provider may give you instructions regarding your medication. You may also be directed to use your inhaler (or another treatment) so your medical team can assess how well it is working.

A lung infection or exposure to cigarette smoke can affect your results, too. It's important that you discuss these issues with your healthcare provider before having your test. If needed, your FVC may be rescheduled.

Timing

The FVC test itself should only take a few minutes. Be sure to ask your medical team how long you should expect to spend at the testing site.

There are other aspects to pulmonary testing, such as functional residual capacity (FRC), which measures air in your lungs after exhaling. You may need other tests if your pulmonary condition has been difficult to diagnose or if you are not improving as expected.

Your whole battery of tests could take an hour or longer.

Location

You will have your FVC test in your healthcare provider’s office or at a pulmonary testing laboratory.

What to Wear

Be sure to wear loose clothing so that you will not feel restricted when you are breathing. It is important that you can inhale and exhale as deeply as you can during the test.

Food and Drink

You will not have to make any adjustments to your food and drink prior to or after having an FVC test.

Cost and Health Insurance

The price of this test can range between $40 and $80. If you have health insurance, your carrier may cover all or part of that cost. Be sure to check with your insurer to ask whether you will have to pay a co-pay or the whole cost of the test.

Keep in mind that if you are having other pulmonary tests, your total cost will be higher.

What to Bring

Bring a list of all of your medications, a form of identification, your health insurance information, and a form of payment.

Also, bring your inhalers with you, even if you have been instructed not to use them prior to your test. You may be asked to use your inhaler during your test.

Recap

Your healthcare provider will let you know if you should use your inhaler or other medicine before the test. The FVC test will likely take just a few minutes. It's usually done in your healthcare provider's office or a pulmonary testing laboratory.

During the Test

When you arrive for your test, you will be asked to sign in and provide your paperwork. You will meet a medical team, which may include a technician, nurse, and/or doctor.

Throughout the Test

Spirometry is non-invasive and only takes a few minutes. Other pulmonary function tests will likely be performed at this same appointment.

FVC spirometry is performed as follows:

  1. You are seated in a chair and asked to breathe comfortably.
  2. A clip is placed over your nose.
  3. You are given a tube to breathe into.
  4. Sealing your lips tightly over the tube, you are asked to inhale as deeply as possible. You then exhale as forcefully as you can.

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

Post-Test

You will most likely not need any recovery time after you have completed your FVC test. You will typically need the same care and support after the test that you usually need. If you have severe lung disease, that support may include supplemental oxygen or caregivers to help you get around.

If you feel dizzy or short of breath, be sure to tell your medical team. You may be asked to sit for a few minutes as you recover.

Additionally, if you are having persistent or serious symptoms, you might need to have your oxygen level checked. If it is low, you will be given supplemental oxygen.

Recap

During the test, you'll be given a tube to breathe into, inhaling deeply and then exhaling forcefully. You'll probably have to repeat it three times so they can get an average measurement. If you feel dizzy or short of breath, you may be asked to sit for a few minutes to recover.

Interpreting Results

Your total FVC volume can be compared with the standard FVC for your age, sex, height, and weight. Your FVC can also be compared with your own previous FVC values. This can determine whether your pulmonary condition is progressing or if your lung function is improving under treatment.

Forced vital capacity will be reported in two ways:

  • As an absolute value, reported as a number in liters (L)
  • On a linear graph to chart the dynamics of your exhalation

The normal FVC range for an adult is between 3.0 and 5.0 L.

For children, the expected FVC can be predicted using reference tables that incorporate the child’s height, body weight, and other factors. For example, the standard FVC for an average-size preschool boy is 1.16 L, and 1.04 L for an average-size preschool girl.

FVC also may be expressed as a percentage of the predicted FVC.

Diminished FVC

Forced vital capacity can be decreased temporarily or permanently. A diminished FVC value is a sign of several conditions, including:

  • Chronic obstructive pulmonary disease (COPD), including chronic bronchitis, emphysema, and bronchiectasis
  • Restrictive airway diseases, such as idiopathic pulmonary fibrosis
  • Structural restrictive airway diseases, such as those produced by scoliosis and chest scarring
  • Diseases such as sarcoidosis
  • Inflammatory lung diseases, such as asbestosis and silicosis
  • Lung cancer

FEV1/FVC Ratio

Your FVC value may be used to calculate your FEV1/FVC ratio. The ratio of FEV1 to FVC compares the amount of air that can be forcefully expelled in one second to the amount that can be expelled in total. A normal FEV1/FVC ratio is 70% to 80% or higher in adults and 85% or higher in children.

The FEV1/FVC ratio can help identify whether a pulmonary condition is obstructive (such as with COPD) or restrictive (such as with pulmonary fibrosis). Any change in the FEV1/FVC ratio can provide valuable information as to whether lung obstruction and/or lung restriction is occurring.

While restrictive diseases limit air intake, they do not inherently affect the force of your exhalations. By contrast, obstructive diseases can make it difficult to exhale, but they don’t necessarily alter the volume of your airways.

With Restrictive Diseases
  • FEV1 and FVC will both be decreased proportionally, so that the ratio of FEV1/FVC is equivalent.


With Obstructive Diseases
  • The FEV1/FVC ratio will be less than 70%.

If both the FEV1/FVC ratio and FVC are low, the individual has a mixed defect with both restriction and obstruction.

Follow-Up

You may need to have further testing after your FVC is done or after your FVC/FEV1 ratio is calculated.

For example, respiratory symptoms with a normal FEV1/FVC ratio suggest a restrictive pattern. You may need to have full pulmonary function tests and imaging tests, such as a chest/lung computerized tomography (CT).

If the FEV1/FVC ratio is low, it suggests obstructive lung disease. Your healthcare provider may repeat the test with a bronchodilator to see if the obstruction is reversible. An obstructive condition such as asthma tends to be reversible, whereas a condition like COPD is not.

Once you are diagnosed with a lung disease that affects FVC, you may need this test repeated periodically. That way your medical team can continue to monitor your condition.

Recap

Follow-up tests may include pulmonary function tests, a chest/lung CT scan, or bronchodilator tests. These can help to narrow down what type of obstructive or restrictive lung condition you have.

Summary

An FVC test helps evaluate your lung function. It measures how much air you can forcibly exhale after taking a deep breath. This helps determine whether you have an obstructive lung condition, which makes it hard to exhale, or a restrictive condition, which makes it hard to inhale.

When you take the test, your doctor will ask you to breathe into a tube. You'll take a deep breath and then blow out as forcefully as you can. You may be asked to bring your inhaler to your appointment to see how it affects your lung function.

Afterward, your healthcare provider may request follow-up tests, such as imaging, to help diagnose your condition.

A Word From Verywell

While FVC is a valuable measurement in evaluating lung disease, it is important to remember that it is just a number. Your healthcare provider will look at your medical condition, your general health, and other findings. That will help them understand how your FVC measurement fits into the big picture of your health.

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5 Sources
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