Yes! This may help you out with the full genetic testing issue too! It is very common to do a fecal fat test to figure out if a person is pancreatic sufficient or not <b>AND to help figure out if a person has CF or not</b>.....trust me, with all you are going through right now, having the GI doc order this test is a very good thing!
Of course, if the test comes back negative (normal) that means you child is pancreatic sufficient, (which health wise is a very good thing) but that would push them farther away from the CF question if it comes back normal -- but do keep in mind if it comes back normal, there are still approximately 20% of people with CF who are pancreatic sufficient (both my kids have normal sweat test numbers and are pancreatic sufficient), so don't let them tell you it means you do not need to move forward with genetic testing to rule out CF.
And, the best news of all is if he is pancreatic insufficient and you start her on enzymes she will start gaining weight and feeling better! At least it will be one piece of the puzzle solved for you!