Kelly, there are no words to properly express how concerned you are. My daughter is due to have her A1C rechecked this month due to a possible elevation a couple of months ago. Her CF doctor didn't make anything of her value but her nutritionist looked at the value incredulously! Nice that the nutritionist was concerned but her doctor wasn't! At any rate, her doctor said that the CFF is likely going to drop the A1C value as a diagnostic tool for CFRD. It can be elevated in times of illness (a chronic state for CFers it would seem as they fight bacteria in their lungs!) and the pre and post prandial values may be more telling.
My daughter's nutritionist was convinced she had Celiac disease due to proper enzyme dosing/administration and poor weight gain. We ruled that out over time and changes in her stool that weren't related to anything Celiac. She also thought her poor weight gain was due to CFRD due to her possible elevation in A1C. Our dietician has the habit of focusing on the "rare" occurrences (e.g., CFRD in a 2.5 yr old like my daughter) and forgetting to pursue other avenues for weight gain. In my opinion, her dietician hasn't been the most helpful - rather, she's had us freaked out about various concurrent illnesses unnecessarily it seems. However, weight gain is important (obviously!) and does relate to lung function...any possible cause for poor weight gain should be pursued. <img src="i/expressions/face-icon-small-sad.gif" border="0">
At any rate...I feel your pain. What we're finding more success with is giving our daughter her enzymes during her meal (i.e., beginning, middle, end). She isn't on a PPI at this point, but I do know how common it is for CFers to take a PPI to improve enzyme efficiency. She's been on Pancrease MT4s, Creon, and Zenpep. Creon was AWFUL. Also odd how some individuals do well with one enzyme and another does quite poorly. Zenpep has been comparable to Pancrease, but I do believe her weight gain has improved since moving from the Zenpep5's to Zenpep10's (perhaps the "time-release" component is better with the larger beads?).
Lastly, CFRD is not the same as Type 1 or 2 diabetes. It's easier to manage and these individuals aren't prone to the many other issues that often accompany diabetes (e.g., circulatory problems, etc.). Having no CFRD is ideal...but, know that if this is the answer to Marty's poor weight gain, he'll quickly get on track with weight gain.
There are just no simple answers. I'll be praying for your little guy!!