well to diagnose it is easier these days.
do a 10 -12 hours fasting sugar test, and the range should be 4-5.6mmol/L
and do another one 2 hours right after your usual meal and that should not be more than 8.8mmol/L

other than that, u could probably do a HbA1C test every 3-6 months to get the average blood sugar for the past 90 days.