Understanding Your FEV1/FVC Ratio

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:

• Forced expiratory volume in one second (FEV1): The volume of breath expired with effort in one second
• Forced vital capacity (FVC): The full amount of air that is expired with effort in a complete breath

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.

Purpose of FEV1/FVC Test

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

Restrictive lung diseases are those that limit your ability to inhale due to reduced lung volume. Examples include:

• Idiopathic pulmonary fibrosis (IPF)
• Sarcoidosis of the lungs
  
• Acute interstitial pneumonia (AIP)
• Hypersensitivity pneumonitis
• Systemic sclerosis (scleroderma)
• Pulmonary vasculitis
• Pulmonary Langerhans cell histiocytosis
• Exposure to inhaled inorganic particles (leading to things like asbestosis or black lung disease)
• Exposure to inhaled organic particles (leading to things like farmer's lung or hot tub pneumonitis)
  

Obstructive Lung Diseases

Obstructive lung diseases are those that reduce your ability to exhale due to obstruction or dysfunction of the airways. Examples include:

• Asthma
• Chronic obstructive pulmonary disease (COPD), which includes emphysema and chronic bronchitis
• Bronchiectasis
• Cystic fibrosis (CF)
  

Risks and Contraindications

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:

• Acute chest pain or recent stroke or heart attack
• Pneumothorax (collapsed lung)
• Recent eye, chest, or abdominal surgery (as deep breathing increases pressure that can affect sutures or vulnerable tissues)
• Aneurysm (a weak, bulging blood vessel in the heart, brain, or digestive tract)
• A recent or current respiratory infection like pneumonia or tuberculosis

Interpreting Results

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:

• Normal: Airflow and lung volume are within the expected range.
• Restrictive: Airflow is normal but lung volume is decreased.
• Obstructive: Airflow is decreased but lung volume is normal.
• Mixed: Airflow and lung volume are both decreased.

Normal FEV1/FVC Ratio and Normal FVC

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.

Decreased FVC

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:

• Deformities of the chest: Associated with scoliosis and other congenital defects
• Lung cancer surgery: In which surgeries like lobectomy reduce lung volume
• Neurological disorders: Such as amyotrophic lateral sclerosis (ALS) which limits lung expansion
• Pleural effusion: In which fluid between the lungs and chest wall reduces lung volume
• Ascites: In which fluid buildup in the abdomen caused by liver disease decreases the available space in the chest cavity

Decreased FEV1/FVC Ratio

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:

• Tracheobronchomalacia: The collapse of weakened trachea (windpipe) as a person breathes
• Constrictive bronchiolitis: A condition in which the scarring of the airways causes them to narrow and become less effective
• Neuroendocrine cell hyperplasia: A rare inherited disease that affects the function of the airways, leading to rapid, difficult breathing

Decreased FEV1/FVC Ratio and Decreased FVC

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.

Assessing the Severity

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:

Follow-Up

Your follow-up is determined by the results of the test, as well as your symptoms, medical history, and other diagnostic tests.

• If a restrictive pattern is observed, healthcare providers will usually recommend more extensive pulmonary function tests to further characterize your lung disease.
• If an obstructive pattern is found, the next step is usually to recommend treatment with a bronchodilator. This is a medication that helps to reduce constriction of the airways.

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.

Summary

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.