Who is right on diagnostic levels, the qualified nurse, or your brother?
Let's see, the WHO criteria for diagnosis of diabetes say only random blood sugars (that is, not a fasting blood sugar, over over 11.1 should raise a concern for diabetes -
https://www.diabetes.org.uk/profess...nitoring/new_diagnostic_criteria_for_diabetes
So, it kind of looks like the nurse is right. Which, let's be honest, shouldn't be suprising that a qualified nurse is rather more familiar with the diagnostic criteria for diabetes than your brother, whom I'm assuming is not medically trained.
If you are concerned about diabetes, see your GP for a hba1c test.