I'm not trying to question what you know about dogs and blood test do tend to take a few days at least to come through, but you can get test blood sugar levels in seconds.
My brother is a diabetic and all it takes is a little drop of blood on a little strip that you wang into a device that reads whether or not your blood sugar levels are high or low, it literally takes seconds to find out.
I shouldn't imagine that it'd change that dramatically to test a dogs blood sugar levels.
and i would imagen the sugar levels would be all over the shop due to any poisioning ,just my thoughts ,