This is a video for something you may find interesting. Basically when your blood sugar rises it changes color. It's intended for those diagnosed with diabetes, but I can see it's use in diagnosing the condition, and for keeping tabs on one's blood sugar. At present it means a permanent tattoo, but should it be possible with temporary ones it may well make a doctor's visit a different thing indeed.
Heck, now that I think of it, felt tipped pens one would use to write on one's skin to keep tabs on blood sugar levels and possibly other matters.