Understanding spirometry: FEV1 normal range

For patients suffering from pulmonary conditions, understanding spirometry measurements is an effective way of being aware of their health status and actively adjusting their lifestyle and behavior in a more educated way.

FEV1 is one of the most relevant parameters measured via spirometry test. In this article, we will examine what it stands for and how to interpret the results.

What is FEV1

The acronym FEV1 stands for Forced Expiratory Volume in 1 Second. It indicates the volume of air a person can forcefully exhale in one second. This parameter is key to assessing the presence of obstructions in the airways that can lead to issues like chronic obstructive pulmonary disease (COPD), asthma, and other respiratory conditions.

Normal FEV1

First of all, it is worth specifying that it is not medically correct to use the expression “normal range” when it comes to FEV1 in spirometry, as it would be more accurate to say “predicted values”, since the FEV1 index results in precise values based on the anthropometric data of each patient. In this article, therefore, we will use the expression “normal values” in reference to its use in everyday language, always keeping in mind what has just been specified.

That being said, there is no straight answer when it comes to defining normal values for FEV1, as they may vary in range according to several factors like sex, height, and ethnicity. In addition, lung function tends to decline with age, so normal FEV1 values decrease over time. In order to get an accurate picture of a patient’s health status, spirometers are usually calibrated accordingly before the test, so that the measurements can be compared to the so-called reference values for each specific case, and the obtained results are presented as a percentage of the predicted value.

FEV1: normal spirometry values by age

Normal FEV1 ranges usually vary with age, and are approximately valued as follows:

• 20-30 years: normal values fall between 80-100% of predicted value. Young adults may show even higher function, sometimes hitting 120%
• 30-40 years: normal values fall between 70-100% of the predicted value
• 40-60 years: normal values fall between 75-100% of predicted value, though decline may already begin for some patients older than 50
• 60-70 years: normal values fall between 70-90% of the predicted value
• Over 70: normal values fall between 60-90% of predicted value

When to worry

FEV1 values lower than the predicted values are indicators of respiratory issues, whose severity may depend. As a general example, here is how severity is calculated in adult males aged 20-60 according to the FEV1 index:

• 80% of predicted value: lung function is acceptable
• 79-71% of predicted value: mild lung impairment (stage 1 COPD)
• 50-70% of predicted value: moderate lung impairment (stage 2 COPD)
• 30-40% of predicted value: severe lung impairment (stage 3 COPD)

Anything less than 30% is considered very severe.

Normal FEV1 by capacity

Other than a percentage, FEV1 may also be expressed in liters. In this case, predicted FEV1 values can vary according to different factors such as:

• Sex: males generally have higher FEV1 values than females
• Height: taller individuals have higher FEV1 values than shorter individuals
• Age: younger adults have higher FEV1 values than older adults

For a healthy man aged 20-40 with a height of 175 cm, FEV1 will be around 3.5-4.5 liters. Values may drop to 2.5-3.5 liters after age 60.

In a healthy woman aged 20-40 and 160 cm tall, FEV1 will be around 2.5-3.5 liters, with an expected drop to 1.5- 2.5 liters after age 60.