Thought I'd add, I'd push for not only a cf genetic test, but one that checks for all known mutations versus a panel. There's good medical justification for this, with the link between borderline sweat levels and having even more rare mutations.
Also, there is no reason to wait three months on a sweat test. They can in fact do it the next day and I even think i've heard of people having both the same day. When I first read the post, i missed your childs age and i thought perhaps you had an infant and they were wanting to wait and see if the sweat level increased with age, but at 5 that really doesn't make sense.
With a 51, the doctor should be even more concerned than he was when he raised the issue of testing. However, many pediatricians and general practitioner types really don't understand the testing. If you don't get the response from him that you think is appropriate to protect your daughters health, I'd consider contacting either the CF clinic in your area (or the closest) or a pediatric pulmonologist who might be better able to help yall figure everything out.
Best of luck!
