The earlier that diabetes is caught, and a person makes the right lifestyle/treatment changes, the less chance there will be of complications. The best way to determine if one is a diabetic is a full glucose tolerance/a1c test. One single blood test, even if fasting, may not be enough for an accurate diagnosis. Stress, for example, can raise glucose levels. I test higher when I'm undergoing something stressful in life. Most doctors would use a glucose level of greater than 200 mg/dl two hours after taking the glucose test liquid, combined with an a1c of greater than 7.0, as a threshold diagnosis. Or 7.5 depending on whether they follow the ADA or the AACE protocol. Not sure which one uses the higher standard.