I know advice about the sweat test may be confusing, especially when that is all that the medical community seems to know about! The sweat test <i>can</i> result in a CF dignosis. In that regard, I don't consider them a waste of time. I don't know the statistics about false negatives where the patient does indeed turn out to have CF.
False <i>positives</i> are linked to a couple other rare diseases/situations that I can't remember at this time.
I just wanted to try to explain that many on here get impatient with the sweat test because they worry that a false <i>negative</i> will prevent doctors and/or parents from continuing to pursue a CF diagnosis, even though a child still has symptoms. Many of us have been down the "you are crazy, your child is not sick" path.
The sweat test can be difficult to administer and that is one of the reasons for false negatives. A full genetic screening is the best way to determine CF.
Sometimes it is hard enough to fight to get the sweat test done, much less genetic testing. So I would just say that if the sweat test is negative yet you are still concerned about your child's health, by all means pursue genetic testing. Good luck!