You are diagnosed with diabetes with test as fasting plasma glucose test, oral glucose tolerance test, and random plasma glucose test. A fasting plasma glucose or FPG test measures a persons blood glucose after an overnight fast of about 8 hours and proves useful to diagnose diabetes and pre-diabetes. Persons with blood glucose level of 100 to 125 mg/dL have pre-diabetes, while a 2 time repeat reading of blood glucose 126 mg/dL or above conforming diabetes.
An oral glucose tolerance test or OGTT is a measure of a persons blood glucose after an overnight fast of 8 hours and 2 hours after he has drunk a glucose beverage with 75 grams of glucose dissolved in water. It is to be noted that a reading of 140mg/dL to 199mg/dL indicates pre-diabetes, while 200mg/dL and above indicates diabetes.
Lastly a random plasma glucose test measures blood glucose at any time of the day. A random blood glucose level of 200 mg/dL or higher with presence of symptoms like increased urination, increased thirst, fatigue, blurred vision, increased hunger, sores that do not heal and unexplained weight loss could indicate diabetes.