I had them open my bag once, look at the machine and say 'blood test?' I said yes, even though I knew that they were assuming blood glucose. Makes no difference to me what they think it is. I've been through security at least 40 or 50 times in the last 3.5 years with no trouble. They recognize it as a medical device. If you're ever questioned, just politely tell them what it cost, what the possible consequences are of not having it, and that it cannot ride in an unheated baggage hold because the LCD will freeze and crack, not to mention whatever internal vulnerabilities it may have.
You've probably discovered this already, since you posted so long ago, but I thought I'd answer in case anyone is ever looking back at the thread.