Diabetes/hyperglycaemia is a pre-operative risk factor for surgical site infection, so D is true. A is false: oral hypoglycaemics are stopped on the morning of surgery (metformin the day before) and only half the usual insulin dose is given. B is wrong because poorly controlled diabetes is a reason to delay elective surgery, and C's target and unit conversion are not from the sources (12 mmol/L is about 216 mg/dL, not 263).