How is prediabetes diagnosed?

Doctors can use either the fasting plasma glucose test (FPG) or the oral glucose tolerance test (OGTT) to detect prediabetes. Both require a person to fast overnight. In the FPG test, a person's blood glucose is measured first thing in the morning before eating. In the OGTT, a person's blood glucose is checked after fasting and again 2 hours after drinking a glucose-rich drink.

Prediabetes is diagnosed by a fasting blood sugar of 100 to 125 mg/dL.

Your doctor can look at a couple of things to diagnose prediabetes. The main thing usually used to diagnose this is a blood draw looking at your fasting blood sugar levels (typically after at least 8 hours without food or drinks other than water); between 100-125 mg/dl is considered prediabetes, and anything above this on two occasions is considered diabetes. Sometimes a hemoglobin A1C is also checked, which gives your average blood sugar level over a 3-month period. If this is between 5.7% and 6.4%, the person is also considered to have prediabetes.