Having just returned from successfully summiting Mt. Kilimanjaro via the Machame route, I want to post some comments that may be of interest to others planning this or a similar adventure.
I use an insulin pump, and prior to departing, I acquired a travel loaner pump as a back-up. As well, however, I took Humulin N and syringes along with my Nova-rapid. Although I have no diabetic retinopathy, I had a dilated pupil examination to insure I was at no greater risk for High Altitude Retinal Hemorrhaging.
Due to the reports of acetazolamide (Diamox) potentially increasing the risk of ketoacidosis, I was reluctant to take this unless I began to feel the effects of altitude sickness. Instead, I opted to take 1200 mg of Ibuprofen daily, beginning on the second day when we reached 3847 meters (12,621 ft.), as there is some evidence it may help prevent AMS. I was fortunate not to suffer from any problems with acclimatization.
According to my BG meter, my blood sugar control was excellent throughout the climb. Of course, I carried dextrose tablets in my day pack and had a supply of trail mix as well. Although there is evidence that the accuracy and reliability of meters are affected by cold and altitude, I felt no evidence of hypoglycemia, and if my BG did rise a bit high after eating, hiking soon brought it down. As the temperature dropped, I insured my BG meter and insulin were well protected in the pack and I put them into my sleeping bag to keep them warmer overnight. My pump was reliable throughout the climb.
From my experience, I would not hesitate to encourage more people with diabetes to undertake similar adventures!