​A change in blood sugar level leads to a condition called diabetes, of which close to 80 million Indians are suffering from. So when is your blood sugar high enough to cause diabetes? Fasting blood sugar more than 125 mg/dL is considered to be diabetic and blood sugar between 100 to 125 mg/dL is considered to be prediabetes. Fasting blood sugar is the gold standard test for diabetes because the body is devoid of any sugar before the test. Not fasting before the test might spike your glucose level and not give an accurate measurement of your blood sugar.​