Dear Katie,
here's my understanding and hopefully others can help too. Generally to have CF you need 2 mutations. There are over 1000 but usually they only test for the most common at first. The delta F508 is one of the most common. so they are going to be looking for one of the much rare ones. If he has one of the rarer ones than they will likely diagnosis with CF. BUT several things to keep in mind: If his sweat choloride is borderline then his genes are functioning somewhat. The fact that he is 9 before the diagnosis means that's true too, so most likely he'll have a less serious form. And once you know you can treat! But the blood test could also be negative. There are rare cases where someone has one gene and is considered CF, but again very very rare, so just having the one delta f508 does NOT mean he has CF.
Our son has two copies of d508. And I know how hard this wait is. We knew that he had 2 copies from new born screen but I had no idea what that meant and i asked both our peditrician and brother-in-law if that meant he had CF and first said "no, it is a screen" and second hemmed and hawed and wouldn't answer point blank. It was horrible. I wanted the facts. This disease sucks BUT there is a ton they can do to keep your son healthy IF he has it AND they are so close to a "CURE". But the one copy of delta 508 does not mean he has CF.
Please write more if there is anything more I can tell you and I'm sure others with more experience can add/or modify anything they think. I'm just trying to put out there my understanding of it.
