I guess you can probably play piano with your feet, too. It may not sound all that great, but, boy, wouldn't that make an interesting picture?
Sorry that this digressed as far as it has.
I saw an instructional video at a medical supply company that cautioned against using fingers that had callouses, scars, or other areas of skin thickness for blood testing. I'm guessing that, as a guitar player, you've probably got the kind of surface on your fingers that would make getting a good incision (and a good drop of blood), somewhat difficult. You may want to try the least used fingers (pinky?) -- and, perhaps, the heel or side of the hand - you probably have plenty of capillary resources there, it may not be too hard to get a drop of blood from there, the wound may close fairly quickly, it may give you an accurate reading with your meter. Of course, these systems are designed for fingers - if you can find a good, usable one, this would be the best option.