Explain how my PFTs went from 111% last month to 94% today


New member
I'm sad and confused. How does this happen?? Last time I got my PFT was from my general doctor using some fancy handheld one I got 111% , and now at my CF clinic with their bulky computer and special nose plug and what not I scored 94%. It's depressing and confusing.

explaon this to me please!

the only thing that has changed since the PFT done a month (and a half) ago and now is I go to the gym 4 days a week whereas before I'd go 3 days a week.

For for the past few days, it's been remarkably windy btw. Everyone here has been talking about how it's so windy and we even had a little dust storm (that was video taped and put on the news). Just something to consider. Oh and my back hurts and my abs are sore from working out.


Super Moderator
Different machines likely have an impact, as well as the nose plug if the GP didn't use. If your CF ones are consistent, I don't think you should be concerned, but of course continue to keep up with meds and working out etc.


New member
I was told years ago that different machines produce different results. Now, this was 10 years ago and things might have changed, but different computers use different algorithms. Different computers might have different settings.

Like Aboveallislove said, stick with the values you get at the CF clinic. Those will have the most comparable variables. As long as those are still good, then you should be okay.


Super Moderator
As the others have said different machines can give different results. I would tend to go with the results from your CF clinic. Sometimes your pfts can go down even though you don't feel bad. That's happened to me. Keep on top of your treatments and exercise. If you're worried about it then add in an additional vest or chest pt session into your day and see if that helps.


New member
My local hospital's spirometer is the same for me as the CF Clinic's spirometer (I use nose plugs for either location). Is the liter value of your PFT different or just the % value? I was under the impression that the % has more variability in the calculations than the liter measurements. That being said my older CF brother always claims he get different PFT results based on many factors like weather, hydration, recent sleep pattern, stress levels at work, time of year, etc. So some of that might be in play.

Oh and sorry your PFTs are down, that always make me feel sucky no matter what the reason.


Yep, happened to me. A different machine in a different clinic gave me a 5-6% lower value. I was pissed! I made sure never to use the "bad" machine again :) (had to do with when I was scheduling appointments!)


New member
Something to consider as you move through teen years into a young adult, different ages have different pft standards, just from my CF clinic experiences.
This is only an example as I don't know what/when the current happen... I remember when I turned 18(adult, hah) I had about a 20% drop in pft's because they classified me as an adult in the computer system. I've never been above 80% since.