The results of a PFT really depend a lot on the effort of the individual taking the test and especially, and probably most importantly, the experience and expertise of the person who is giving the test. I've had many PFTs over the last 20 years, and it really depends a lot on how well you are coached through the tests, assuming everything else is equal. Many things besides can influence the results: how you feel, how well you slept, how long it's been since you took your meds, if you're sick, is it a good breathing day or a bad one.....those things make a HUGE difference in the results.

When you say completely different results, are we talking one result mild COPD and the other result very severe COPD? Or something else? What makes you think the results are "completely different"?

Sorry Wizard. Not being a doctor makes a lot of these things a mystery for me too. My lung doc would not let me take the test for three weeks after a hospital discharge. He didn't want the poor results on my record for the Disability Board.
BUT having both results may not be a Bad thing for you - IF you can remember (in detail) how you felt on those separate days. Because the PFT measurements are a comparison to some Norm, you can find a "sweet spot" to shoot for in your day to day activities. Hope this helps some.

Even though I received my diagnosis of COPD I have never been tested by a pulmonologist. I was on a trial and error until I started using Trelegy. I feel so much better. I don't know what to tell you except do one more test and I will keep you in my prayers.