How to Read Your Spirometry Test Results
The FEV1/FVC ratio is a test that helps measure how much air you can forcefully expire (exhale) from your lungs. It involves a tool called a spirometer that can deliver two specific measurements: Plastic Film Extrusion Equipment
The test can help diagnose and monitor restrictive lung diseases (in which you have difficulty inhaling) or obstructive lung diseases (in which you have difficulty exhaling).
This article discusses the purpose of the FEV1/FVC ratio and its use in diagnosing and treating lung diseases. It also explains how the results are interpreted and what follow-up tests may be needed.
If you have been diagnosed with a pulmonary (lung) disorder, you will undergo a battery of tests, including the FEV1/FVC ratio. The FEV1/FVC ratio can help determine whether your condition is restrictive or obstructive and how severe the restriction or obstruction is.
This test can also monitor lung disease. Measuring your FEV1/FVC ratio at regular intervals can help assess how well treatment is working and whether your condition is progressing, improving, or remaining stable.
The FEV1/FVC ratio is just one of several measurements taken with a spirometer (a handheld device that measures the volume of air expired or inspired by the lungs). The test can be performed in a healthcare provider's office and takes about 45 minutes to complete.
Restrictive lung diseases are those that limit your ability to inhale due to reduced lung volume. Examples include:
Obstructive lung diseases are those that reduce your ability to exhale due to obstruction or dysfunction of the airways. Examples include:
Spirometry is a safe, non-invasive test. It involves breathing into a tube attached to a meter that measures the volume and/or force of airflow.
There are few side effects associated with spirometry. Some people may feel lightheaded, have shortness of breath, or cough when blowing into the spirometer. If you have asthma, there is a small risk of an asthma attack.
Spirometry may not be recommended in people with the following conditions:
The FEV1/FVC ratio is expressed as a percentage (%). A result is "normal" if the percentage is at or above the predictive value for your age, height, and sex.
Percentages below the predictive value are considered abnormal. The lower the percentage, the more severe the lung condition generally is.
By comparing the FEV1/FVC ratio to the total volume of air in your lungs (FVC), your healthcare provider can determine whether your condition is:
At first glance, a normal FEV1/FVC ratio and normal FVC might suggest that you have no problem, and, in most cases, that would be right.
However, once-off spirometry doesn't always expose conditions like mild to moderate COPD. In some cases, the FEV1/FVC ratio can veer between normal and abnormal values (referred to as "diagnostic reversals"). Some studies report that as many as one in five people with mild to moderate COPD fall within this category.
Because of this, repeated spirometry may be needed to return an accurate result.
People with asthma may also have a normal FEV1/FVC ratio as well as a normal FVC outside of an asthma attack. In such cases, a bronchoprovocation challenge may be needed to induce asthma symptoms with inhaled chemicals or cold air.
If your FVC is decreased but the ratio of FEV1/FVC is normal, this indicates a restrictive lung condition. Restrictive problems occur when a person can't inhale deeply due to the loss of lung capacity.
In addition to restrictive lung diseases, a decreased FVC may be due to:
A decreased FEV1/FVC ratio with a normal FVC indicates an obstructive lung condition. The diagnosis is usually reached when the ratio is less than 70% in adults and less than 85% in children.
Damage or dysfunction of the airways is associated with conditions such as asthma, COPD, bronchiectasis, or cystic fibrosis. Uncommon causes of pulmonary obstruction include:
When both the FEV1/FVC ratio and FVC are decreased, it is a sign of a mixed defect involving obstruction and restriction.
This can occur when a long-standing lung disease like sarcoidosis causes scarring that distorts the airways while reducing the overall volume of the lungs. Overlapping restrictive and obstructive lung diseases can do the same.
A mixed defect may be the result of co-occurring pulmonary and non-pulmonary diseases (such as COPD and heart failure) which cause direct damage to the airways and indirect damage to the lungs.
If the FEV1/FVC ratio is found to be abnormal, the next step is grading the abnormality to determine the severity of the condition. The American Thoracic Society has set specific guidelines for this:
Your follow-up is determined by the results of the test, as well as your symptoms, medical history, and other diagnostic tests.
If you are being treated for obstructive lung disease, your healthcare provider will most likely monitor your progress by retesting your FEV1/FVC ratio.
If the ratio improves with a bronchodilator, that means that the obstruction is at least partially reversible. This is usually seen with conditions such as asthma.
If the ratio does not improve with a bronchodilator, it may be irreversible, such as is often seen in COPD.
With restrictive lung conditions, your healthcare provider may recommend more pulmonary function tests. For obstructive lung conditions, your healthcare provider may retest your FEV1/FVC ratio. With some conditions, like asthma, your ratio may improve after using a bronchodilator.
The FEV1/FVC ratio indicates how much air you can forcefully exhale. It's measured by spirometry, a test used to diagnose or monitor lung conditions. The FEV1 measures how much air you can exhale in one second; the FVC measures the total amount of air you can exhale forcefully in one breath.
Your healthcare provider can use the FEV1/FVC ratio to help determine if you have a restrictive or obstructive lung condition.
If you have a restrictive condition, you may need more pulmonary function tests to help diagnose your condition. If your lung condition is obstructive, your healthcare provider may recommend using a bronchodilator. It is also possible to have a mixed defect in which there is both restriction and obstruction.
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By Deborah Leader, RN Deborah Leader RN, PHN, is a registered nurse and medical writer who focuses on COPD.
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