Lung Function


New member
I am seeing so many people post about their lung function. I see that some people have a lung function of 125%. Others say they have almost perfect function at 97%. Does anyone have any information on how this works? My son in law has a lung function of 71 and is 21 years old. How does that relate to non cf lung function? Thanks for your help!


New member
Lung function is stardard measurement for everyone, c.f. or not.

As a teen I was always in the high 90s and for most people with c.f. that tends to decline with age.

Ways to halt the progression are the usual antibiotics, airway clearance, etc.

If he is in his 70s it isn't likely he'll go back up unless he had a recent lung function decrease caused my excess mucus. If that is the case, he can get tuned up and go back to his baseline.

However, if it was a gradual decrease over time that would be most likely considered lung scarring and so far only transplants can fix that.

All the best


New member
Lung function above 70% is sometimes considered mildly diseased. 40% to 70% would be moderately diseased and lung function below 40% is sometimes considered severely diseased. But this doesn’t really tell the whole story.

Lung function is truly measured in volume. FEV1 is the volume (typically liters) that a person can forcefully exhale in 1 second. FVC is the amount of air volume forcefully exhaled after a full inspiration. To give these volumes context, the labs are reported as a comparison against the population of healthy individuals with similar gender, age, and size. This is reported as FEV1% or FVC%. So a person that blows an FEV1% of 100% is at the predicted volume for their gender, age, and size. But like any average some people are naturally above and some are naturally below.

What seems to be more important for an adult with CF than just basic percentage, is where lung function is compared against recent tests (like the past 3-4 PFTs). It is also important to consider where they are at relative to their personal baseline. Baseline is the highest or best test ever (with the caveat that many CF folks have significant lung damage prior to reaching their mature size). For example my baseline FEV1% is 108 which I blew in my mid 20s. But I’ve dropped 14% since then. This drop indicates that my disease is slowly progressing. Another CF-person might have a baseline of 90% but in a decade might only drop to 85% therefore their disease is progressing slower than mine despite the fact that I have better lung function percentage. The key to CF health and the goal of our lung-centric treatments is to minimize lung function decline.


Super Moderator
Great summary, Ethan. Thanks so much for spelling out these basics for us all. And yes, from my understanding, trending is one of the most, if not THE most, important factor. Which way is your lung function going and at what speed. Different numbers for different people based on a host of factors, but what is your trend and rate?


Active member
Lung function testing is based upon a "average" person of the same age, height, weight and sex. If a person blows 70% it is 70% of what a normal person of his/her like personage would blow. 100% is the base line for comparison.