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F508del/R117H sweat test negative

Dear ladies and gentlemen,
I am 33 years old. As symptoms I have only a slight “mucus feeling” in the throat, that goes away when clearing the voice.
I have had a sweat test done a few days ago and had other values checked. The result of the sweat test was 19 mmol/l. Therefore truely negative. Also the other values were like from a healthy person. A lung CT will be done in the future due to the “mucus feeling” (I am still breast feeding at the moment). I am very glad of course, however I am a bit skeptical. The second mutation is there, indeed.
Can it be nevertheless, that a CFTR caused defect is underlying? Could the sweat test be possibly false negative? Should it be repeated for being secure or other diagnostics should be done? In my CF center they said “definitely healthy” and the lung CT is done for the final security.
Best regards,
the mutation R117H can have two subforms, with 5T and 7T. If you have R117H 7T, it is not CF even if you have the second mutation, as the function of the chloride channel is sufficient (as you can see from the normal sweat test result). In case of the mutation R117H 5T a mild form of CF can occur in men and women, it can however also be possible to have no changes at all, so that you would be healthy in spite of the mutation.
Therefore it makes sense to have a lung CT done, in oder to see, if there are any changes.
As long as lung function and CT are normal, however, yearly controls are sufficient in my opinion.
In case changes should occur, it should be discussed with the center, if you should take probably Kalydeco, that has been licensed in the meantime for this mutation.
Best regards,