Katie,
My son was diagnosed this past September. His genetic testing, and this is with "Quest" full mutation pane was negative, meaning the mutated gene has yet to be identified by scientif methods (hasn't been found yet). However, his Nasal Differential Potential was positive as well as a sweat test that is based on a different channel used in the typical sweat test. As confusing as all the back and forth of no/yes he has CF, coming up with a diagnosis has brought comfort in a strange way and because he is now getting the right treatment his lung fuctions are up.
I will be taking the Nasal potential test in January to see if I have CF. Wouldn't suprise me iat all if I do and it no longer scares me.