Hi. A fasting test cannot properly be used to diagnose diabetes as it does not detect sugar spikes after meals. If it shows up as very high then it does indicate diabetes but if it is normal it does not eliminate diabetes. The standard diagnostic tests are the GTT (Glucose Tolerance Test) or the HBA1C, the latter being the real measure. For this you need to have blood taken by a phlebotomist at the hospital or local surgery. It shows the average blood sugar over the previous 3 months. I was diagnosed with a urine stick; crude but if positive it does indicate sugar in the urine and hence diabetes.