What Is an FEV1/FVC Ratio in Spirometry?

In diagnosing and treating obstructive lung diseases such as chronic obstructive pulmonary disease (COPD), doctors use various tests to determine the severity of the condition. Spirometry is one test that helps measure lung function by analyzing the force of your breath. The ratio of forced expiratory volume in one second (FEV1) over forced vital capacity (FVC), also known as the Tiffeneau-Pinelli index, is a measurement of the amount of air exhaled forcefully in one second compared to the full amount of air that can be forcefully exhaled in a complete breath.

As many chronic lung disorders can appear similar in terms of symptom presentation, the FEV1/FVC ratio is primarily used to help determine whether your lung condition is restrictive or obstructive in nature. Restrictive conditions (such as pulmonary fibrosis) affect one's ability to inhale, while obstructive conditions (such as asthma and COPD) affect one's ability to exhale.

The ratio itself is a more indicative diagnostic tool than either measurement alone, although FEV1/FVC is just one of several measurements taken when using a spirometer.

The test can be done in your doctor's office and takes about 45 minutes.

Spirometry is a very safe, noninvasive test that involves breathing into a tube attached to a meter that measures airflow and force. However, you may feel lightheaded or short of breath if you blow too forcefully, or you may start to cough.

Those who have asthma are at a small risk of having an asthma attack during the test, and there is also a slight risk that breathing with strong exertion could cause severe yet temporary breathing problems. However, since the test is performed under medical supervision, your practitioner will be able to help manage any situations that may arise.

If you have any of the following conditions, a spirometry test is not recommended:

• Chest pain, recent stroke, or heart attack
• Collapsed lung (pneumothorax)
• Recent eye surgery, or chest or abdominal surgery, as deep breathing could affect the pressure in those areas
• Aneurysm (bulging blood vessel) in the brain, chest, or abdomen
• Current or recent respiratory infection or tuberculosis

In measuring FEV1/FVC, the amount of air you exhale in one second is recorded, as well as the total amount of air you are able to exhale. Based on the FVC calculated for your age, height, and weight, the ratio of these two values is then evaluated. The ratio of these two numbers is expressed as a percentage: the percentage of the FVC expired in one second.

If your FVC is decreased but the ratio of FEV1/FVC is normal, this indicates a restrictive pattern. A normal ratio is 70% to 80% in adults, and 85% in children.

Restrictive lung concerns may be those in which the lung tissue itself is damaged, or when structurally someone is unable to breathe as deeply as normal. Some examples include:

• Pulmonary fibrosis, such as idiopathic pulmonary fibrosis, a scarring of the lungs of uncertain cause.
• Deformities of the chest such as scoliosis or chest wall scarring
• Results of lung cancer surgery, such as a lobectomy or pneumonectomy
• Infections and inflammatory diseases such as pneumonia, tuberculosis, sarcoidosis, silicosis, and asbestosis
• Neurological disorders such as amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease)
• Pleural effusion, in which fluid builds up in the area between the lungs and the chest wall
• Ascites: Fluid buildup in the abdomen due to liver disease or cancer in the abdomen can cause a restrictive pattern by limiting the ability to take a deep breath.

If your FEV1/FVC ratio is decreased, this is consistent with an obstructive pattern.

Usually, this diagnosis is reached if the FEV1/FVC is less than or equal to 70% in adults and less than 85% in children. Damage to the airways and/or constriction of the airways is indicative of conditions such as:

• Asthma
• COPD, including chronic bronchitis, emphysema, and bronchiectasis
• Bronchiolitis

If the FEV1/FVC ratio is found to be abnormal, it's important to take the next step, which is grading the abnormality to determine the severity of the condition. The American Thoracic Society has set specific guidelines for this purpose:

If a restrictive pattern is observed, doctors will usually recommend full 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, a medication that helps to reduce constriction of the airways.

If you are being treated for obstructive lung disease, your doctor 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 often seen in COPD.

The FEV1/FVC ratio is just one of several tests that can help diagnose your specific lung condition. It's easy to get caught up in a "good" or "bad" result, but consider that it's just one small piece of information used to evaluate your disease. Your doctor will also look at your general health, lifestyle, and other factors to thoroughly assess your condition and come up with a treatment plan that's customized for you.