What Is Forced Vital Capacity (FVC)?

What to expect when undergoing this test

Lung function test
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Forced vital capacity (FVC) is the amount of air that can be forcibly exhaled from your lungs after taking the deepest breath possible, as measured by spirometry. This test may help distinguish obstructive lung diseases, such as asthma and COPD, from restrictive lung diseases, such as pulmonary fibrosis and sarcoidosis.

FVC can also help doctors assess the progression of lung disease and evaluate the effectiveness of treatment. Your FVC value can be reversibly or chronically altered.

Generally speaking, men will experience a greater decline in lung capacity than as they age compared to women irrespective of the presence or absence of lung disease.

Purpose of Test

FVC is used to evaluate your lung function in a wide range of pulmonary diseases. It does not diagnose specific lung diseases. Rather, it evaluates the impact of lung diseases on your ability to inhale and exhale.

There are many reasons you may need to have your FVC measured, including:

  • You have shortness of breath, a persistent cough, or wheezing.
  • Your doctor wants to assess your respiratory function when your blood oxygen level is low.
  • You have a temporary lung condition (such as pneumonia) or chronic lung disease (such as COPD) that needs monitoring: A change in your FVC value can help determine if your condition is improving with or worsening despite treatment.
  • You're having surgery: It's important to know if breathing is stable prior to a procedure, especially if you will be having lung surgery.
  • You have heart disease and need an assessment of its effects on your ability to breathe.
  • You and your doctor are planning your lung rehabilitation program.
  • You've reached the endpoint in a clinical trial expected to affect lung function.

Associated Tests

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

FVC and VC record similar information because 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, while VC records the maximum amount of air that exhale when breathing normally. Meanwhile, FEV1 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 by comparing your measurements to standards based on your age, gender, race, height, and weight.

Risks and Contraindications

This test 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 FVC). You could potentially use a spirometer the wrong way, exhausting yourself.

After that, you may be instructed on how to use it at home on your own. You should also be sure that the spirometer you use has been adequately cleaned before each use so that you will not be exposed to anything that can cause an infection.

If you have a friend or family member who uses home spirometry tests or therapeutic incentive spirometry, do not use their device to measure your own FVC or for other pulmonary function tests.

Before the Test

Before your FVC test, your doctor may give you instructions regarding your medication. You may be instructed to abstain from certain medications for about one day before your FVC is measured, as they could affect how your results can be compared to previous results. 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, so it is important that you discuss these issues with your doctor before having your test. If needed, your FVC may be rescheduled.

Timing

The FVC test itself should only take a few minutes, but 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), and you may need a variety of 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 doctor'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 take your maximum inspiration and expiration 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

When you go to have your FVC test, be sure to bring a list of all of your medications, a form of identification, your health insurance information, and a form of payment. 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.

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 be likely to 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 and 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. If you have severe lung disease and are dependent on supplemental oxygen and/or caregivers to help you get around, you will need to have the same care and support after your test that you usually need.

But 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. And 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.

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, if applicable, to 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.

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

FVC is important in establishing whether there is a narrowing of the airways (pulmonary restriction). An FVC value that falls below the fifth percentile—meaning that 5% of adults in your age group have a lower value than you—is a general indication of restriction.

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, and 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, suggesting obstructive lung disease, your doctor may repeat the test with a bronchodilator to see if the obstruction is reversible. Conditions such as asthma tend to be reversible, whereas conditions like COPD and pulmonary fibrosis are not.

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

A Word From Verywell

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

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Article Sources

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