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 which 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 used to help determine primarily 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 taken by itself, although FEV1/FVC is just one of several measurements taken when using a spirometer.

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. The test takes about 45 minutes,

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.

Contraindications

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 number of 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. Ordinarily, the two values are proportional. If the FVC is decreased, then the ratio is looked at more closely.

Decreased FVC With Proportional FEV1/FVC Ratio

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 percent in adults, and 85 percent in children. Restrictive lung diseases 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
• 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 ALS
• Pleural effusion, in which fluid builds up in the area between the lungs and the chest wall
• Ascites, a 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.

Decreased FVC With Decreased FEV1/FVC Ratio

If your FVC is decreased and your FEV1/FVC ratio is also decreased, this is consistent with an obstructive pattern seen in lung diseases such as asthma and COPD. Usually, this diagnosis is reached if the FEV1/FVC is less than or equal to 70 percent in adults, and less than 85 percent 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

Assessing the Severity

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, as outlined in the table below.

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 which 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.

A Word From Verywell

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.