My daughter was just diagnosed with CF and even though she wasn't a preemie she's still just a baby. I know exactly what you're going through, when we found out she might have the disease we had no clue what it was or what it meant. we researched it quite heavily and found out that it mainly affects the lungs and pancreas.Theres a lot more to the disease, but this is just basically what happens: ppl that have the disease make thicker mucous that builds up in their lungs making it easier to get infections and harder to get rid of them. And with the pancreas, the body doesn't produce the right enzymes to properly break down food so its harder for ppl with it to get the nutrients they need (hence the poor weight gain). But doctors give medicines to thin the mucous (my daughter is on pulmozyme) and enzymes to help break down food and vitamins. We have yet to find out if she has the pancreatic part because she has been gaining weight just fine (they did a test and we havent heard back yet).
Now that we know for sure CF is what she has we are being very proactive as far as treatment. Even before she shows any symptoms we are treating her. Now I'm not an expert or anything as I've just found out about my daughter (last week) but from what everyone has told me on this site we need to be hopeful. There are lots of medicines and treatments to keep our babies healthy, and my doctor is very encouraged with research that is going on right now and thinks there will be a cure within the next 10-20 years which is well within our babies lifetimes.
The sweat test is no big deal, my daughter just had 2 done. (at the center where we are going) They just put a chemical on their arms for 5 minutes to make them start seweating and then strap a little tube thing on the arm for about 20 minutes to collect the sweat. It doesnt hurt them, my baby was just unhappy because they had to hold her arm down. I don't know if the procedure is different at other clinincs or not.
Hopefully your grandson doesn't have the disease, but if he does you're not alone. My mom is on this site (addysgramie) and she knows first hand how it feels to have a grandchild affected. I know its devistating but we try to take it one day at a time, and every day that shes healthy we are thankful. Good luck! <img src="i/expressions/face-icon-small-smile.gif" border="0">