Daisy..
6.8 mmol/l is sort of an high fasting level, but it does have to be taken into context with many factors before worrying about pre-diabetes..
Firstly is it a one off or constant, could he have a brewing, underlying infection, is he on other medication that might have raised his BG slightly... Is his body stressed in any way, this could be workload, neighbours causing a ruckus, the tackling of the phone bill that's been wrongly charged or even a niggly pain etc... or just in a grumpy mood!
All these factors can short term put up and non-diabetics blood glucose but it doesn't mean they are heading towards diabetes or eve pre-diabetes..
The best way of testing his for a doctor to rule out any underlying cause, several fasting tests week apart, and/or a GTT test to see the reaction of how the body adsorbs glucose!