The problem that our non-diabetic friends tend to forget is that blood glucose levels can and do flutuate and you could have quite an high reading and not be a diabetic even over a short period of time..
If your stress levels are high, you have an infection or fighting a cold etc this can boast the sugar levels, The highest reading I've seen in a non-diabetic has been 16mmol/l the individual had taken a funny turn so parmadic called, standard BG taken on arrival.. But after admittence to hospital more testing within a couple of hours it had returned to normal, further checks up's a couple of GTT's normal BG's :?
If an higher than normal reading is found then yes it does need to be checked out by a HCP so that any underlying cause can be ruled out, and monitored if necessary,