What Is Diabetes?

There are several tests a doctor can perform to check whether you have diabetes. One test, a fasting glucose level test, measures your blood sugar after you have fasted for at least eight hours. At that point, blood sugar should be low — between 70 and 100 mg/dL in healthy adults. A blood sugar reading between 100 and 125 mg/dL indicates possible prediabetes, and a reading of 126 mg/dL or higher suggests that you have diabetes, though doctors will generally repeat the test to make sure. Another test, the random blood glucose test, which doesn’t require you to fast, may indicate diabetes if your blood sugar is higher than 200 mg/dL. A third test, the oral glucose tolerance test, is usually only performed on pregnant women to test for gestational diabetes, or on people suspected of having type 2 diabetes whose fasting blood glucose is normal. It measures how quickly your blood sugar returns to normal after you fast, then drink a sugary liquid. If your blood sugar stays high for a long period of time after the test, you may have diabetes. Finally, hemoglobin A1c (a measure of your blood sugar for a three-month period) now can be used to diagnose diabetes, as well as tell how well you are controlling your blood sugar. Levels of 6.5 percent or higher on two separate tests indicate diabetes.