Abnormal Fecal Fat Results

My four year old has Asperger's, joint pain, abdominal pain, flank pain, and mild asthma symptoms.  He has already been seen by a rheumatologist who saw no sign of arthitis and suggested he be seen by a gastroenterologist.  We took him to the GI in July.  He ordered two fecal fat labs.  Both came back abnormal.  He is now testing for cystic fibrosis and celiac disease.  I am a carrier of the cystic fibrosis mutation delta F508.  My husband's carrier screen came back negative five years ago.  My son is on a GFCF diet except for once in awhile when we go out to eat.  He hadn't had gluten for quite some time before the fecal fat tests were done.
He doesn't really have diarrhea or fever.
Are we wasting our time with the CF genetics test and the celiac labs?  What else could cause these abnormal results given that he doesn't have diarrhea or fever?

[mammo]

There are many other causes of this and they are looking at the most common at this time.  Google this and see all the other causes for his fat levels and make sure they cover everything with the testing.  Take care.

[Gina04]

Got the celiac results back this week and they were all negative.  We are still waiting for the CF genetic screen which I suspect will either show that he does not have any CF mutations or that he is a carrier of the delta F508.  (This is based on the results my husband and I had with ourts.)  I talked the doctor into doing a sweat test as well.  We have that and probably a lactose intolerance test done on Monday.  Again, even though he is probably lactose intolerant (the rest of the family is), I don't think that is the problem because he hasn't had lactose in a long time, being on the GFCF diet.
Thursday, he started coughing up thick mucous and has done so several times since then.  I talked with a genetic counselor at the hospital my screening was done at.  He said that there is a chance my husband has one of the rare CF mutations that doesn't show up on the genetics test.  I'm hoping that if this is CF, the sweat test will be positive so we don't have to do a lot of other tests on him.