I was told that a type 1's blood is "sticky" - doesn't matter how controlled you are but it just is, and therefore this is the main reason why we cannot donate. There is a plastic "snow shaker" gadget in my hospital diabetic unit and one side has water in it with little crystals and they float around easily and on the other side, there's obviously something in it much thicker, so the little crystal pieces take their time moving around and are much, much slower. A DSN explained that this was to show the differences in a non diabetic's and a diabetics blood consistency and our blood is known to be "sticky".