I was dx with CF about 10 years ago, I had many positive sweat tests but I also have a disease that is known to cause false positive sweat tests, Genetic testing reveled Df508 one of the most common genes. I cultured Pa and MRSA several times.
I moved to SC about three years ago and started being seen at MUSC, The doctors there felt that I did not fit the typical CF protocol and that most of my sickness is coming from something else.
They sent my blood work off to Mayo clinic which we were sure was going to come back negative for a second gene, instead it came back with the DF508 and a gene that has never been described before O1330E.
I then went to the University of North Carolina and had one nasal PD test done, it was done in there lab. I had very bad cold that day, figures, my nose was swollen, The test came back completely normal. Of course, thanks to the people on here, I went back and questioned the doctor about my test being normal since I had a bad cold.
The doctor said that the test would not come out normal if my nose was swollen enough to effect the test, it would turn out abnormal, it could still be negative but it wouldn't be normal, apparently I responded perfectly to the test, So 10 years almost of thinking I had CF, and I was undiagnosed.
I am still seen by one of the CF doctors there that runs a non CF clinic, Dr Flume, he is amazing. We don't exactly know what is wrong with me, we know I have severe reactive airway disease to the point of needing to be intubated (life support) if I am exposed to certain things.
Even going there last week, I had no cough, felt great, I was in the building for an hour, I had a rash and was wheezing by the time I left.
UNC is where the Nasal PD was invented
Best of luck to you