Normal fasting blood glucose is 3.5 mmol/l - 4.5 mmol/l
Most non-diabetics will be sub 5.5 mmol/l at +2 hours.. the maximum +2 hour 'normal' range is considered to be 7.8 mmol/l..
One reading does not make a diagnoses and even non-diabetics can exceed the 'normal' range under certain circumstances.. I would suggest however they need to visit their GP for a proper diagnoses.