They used to say that a fasting glucose of 126 or higher was diabetic, and 110 or higher was prediabetic. Late last year the guidelines were changed--now a fasting glucose of 100 or higher is considered prediabetic, or "impaired fasting glucose."

I bought a kit to test mine because I suspected I had a problem. When I started testing, my FBG was consistently in the 100-115 range (argh!). (At the time, I was doing a loose CAD approach, which clearly was not working for my body. A couple days, my BG was down under 75 by dinnertime from not snacking, and then soared over 150 after a "reward meal" dinner that was admittedly not very balanced....)

Having prediabetic FBG levels was a wakeup call for me. That was one reason I decided I'd better get my act together. I switched to a basic low-carb approach on March 7.

Now my FBG is consistently in the 80s or low 90s (and even occasionally in the 70s). FWIW, the Life Extension Foundation says a fasting glucose level of 83 or less is optimal. Initially I thought that was unrealistic, but after 3 weeks of this, I'm getting pretty close. I'm delighted with the 80-90 range.

I highly recommend getting a home blood glucose monitor. You can usually find deals on these--I got a Freestyle monitor free with the (expensive) test strips. I like mine because it can do alternate site testing, like the forearm, instead of the more sensitive fingertips. It is just amazing to be able to check and see what effect a given food is having on my body, instead of just guessing at it. Blood glucose varies, and if you're depending on a lab, you're going to get only a couple readings to work from (if you're lucky) -- if you have a home monitor, you can take as many readings as you want, whenever you want, and get a much more complete picture. This is probably the single best thing I've done to motivate myself to stay on track with low-carb.