When Tim was on the pen for shots, and we switched to the mini needles, he ended up with large ketones and very high blood sugars a lot too. Granted, he is one that gets ketones easily anyway, but this was ridiculous. We finally figured out that the mini needles were too short to use in his upper rump, but fine in his skinny arms. He was much younger (went on the pump when he was in 5th grade) so much skinnier at that time. So you may be able to still use those mini needles in some areas, but not others.