Understanding your pulmonary function test: normal values by age

Pulmonary function tests are quick exams aimed at measuring how well your lungs are working.

They are usually non-invasive and quick and can provide insights into several aspects of your respiratory health, such as how much air you can breathe in and out, how much oxygen goes into your blood, how exercise affects your lung function, or how effective your breathing medications are.

One of the most commonly used pulmonary function tests is spirometry.

An introduction to spirometry

Spirometry is a simple test that helps understand how well your lungs work by measuring the amount of air you can breathe out and how quickly you can do it. It is a key tool in diagnosing and monitoring conditions like asthma, COPD (chronic obstructive pulmonary disease), or other respiratory problems.

However, if you are unfamiliar with the codes and percentages used in spirometry reports, your test results may be confusing and hard to understand. So, let’s break down the key spirometry values and explain what’s considered normal for different age groups.

How to interpret the key spirometry parameters

When consulting a spirometry test report, you will probably come across these three acronyms: FEV1, FVC, and FEV1/FVC. These are the three key measurements of spirometry, and they must be interpreted as follows:

• FEV1 (Forced Expiratory Volume in 1 Second). This measures how much air you can forcefully exhale in one second, and it helps assess how open your airways are
• FVC (Forced Vital Capacity). This is the total amount of air you can blow out after taking a deep breath, and it provides insights into your lung capacity
• FEV1/FVC Ratio. This is the comparison between the amount of air you can blow out in the first second and the total amount of air exhaled. It is key to identify if there’s any blockage in your airways: if your lung capacity is good but you are only able to exhale a little amount of air in 1 second, there may be obstructions like mucus or narrowings that affect your capacity to breathe

Normal VS predicted values: what’s the difference?

When reading your test results, you will notice that each measured parameter is expressed in the form of a percentage. This happens because your results are compared to the so-called predicted values, an average based on large studies of healthy people with similar characteristics to you. These characteristics include age, gender, height, and ethnicity, and spirometers are usually calibrated accordingly.

In concise words, we may say that the predicted values are the expected results for someone like you if your lungs are perfectly healthy. Because every patient is different, spirometry results are expressed as a percentage of the predicted values. A result of 80% or higher is considered normal.

Let’s try with an example. Let’s say your predicted value for FEV1 is 3,5 liters and your FEV1 is 2,8 liters. Since 2,8 is 80% of 3,5, your FEV1 may be considered normal for someone your age, sex, ethnicity, and height.

If you wish to know more about how to read and interpret spirometry results, we explored the topic in a previous article.

Normal spirometry values by age

As said before, age is one of the parameters to take into consideration when measuring lung function. As we get older, pulmonary function naturally declines, as lung tissue becomes less elastic and the muscles supporting the lungs tend to weaken over time. Spirometry takes age into account, so what’s considered normal for a 25-year-old is different than for someone who is over 60.

In general, expected FVC for a healthy man aged 20-30 may fall between 4 and 5 liters, with FEV1 varying between 3,5 and 4,5 liters. Expected FVC for a healthy man aged 40-50 may fall between 3,5 and 4,5 liters, with FEV1 varying from 3,0 and 4,0 liters. The values decrease in older people, with expected FVC between 3,0 and 4,0 liters and FEV1 varying between 2,0 and 3,5 liters in men over 60.

These numbers, however, are rough estimates and will vary based on sex, height, ethnicity, or fitness level.

What to do if your spirometry values are lower than normal

Lower spirometry values may be indicators of underlying issues, although they don’t always mean you have a serious lung disease.

Sometimes, mild abnormalities may be due to temporary issues like an infection, poor effort during the test, or allergies. However, consistently low values, especially in the FEV1/FVC ratio, can point to conditions that may require medical attention and should always be evaluated by a doctor.