Also to add to AOKAY's post - my husband is diabetic and has a meter here. I take my sugar sometimes (no reason, I just like to see what it is) I was going for a blood test and right before I went I took my reading and got 98. I went right to the place to get my blood drawn and when it came back it was 86.
That could be due to the fact that a lab is more sensitive, basically the margin of error is greater on a home device. I'm guessing my glucose was up since I had eaten 9.5 hours prior.