Is a random glucose blood sugar test accurate to diagnose diabetes?

No: Blood glucose goes up and down through out the day. Blood glucose goes up after eating a meal, usually peaking in 1-2 hours and then it goes back down until the person eats again. In people without diabetes the range that blood glucose varies is controlled and usually ranges from 65-145. In people with diabetes, blood glucose goes much higher at times, but will often be in the normal range.

Retest : A random glucose of >200 may suggest diabetes but a second test such as fasting glucose or an glucose tolerance should be done to confirm the diagnosis.

Random glucose >200: The ADA has set criteria for the diagnosis of diabetes as a patient with classic symptoms of hyperglycemia and a random glucose blood glucose > 200mg/dL http://www.diabetes.org/diabetes-basics/diagnosis/