Diabetes Tests

Fasting Blood Glucose (FPG) Test

This is one of the most common and preferred tests; it measures blood glucose in a person who has not eaten anything for at least eight hours. Both diabetes and prediabetes can be diagnosed this way. A blood glucose level of 126 milligrams per deciliter (mg/dL) or higher indicates diabetes.

Random (Non-fasting) Plasma Glucose Test

This measures blood glucose without fasting. This test, along with an assessment of symptoms, is used to diagnose diabetes but not prediabetes. A blood glucose level of 200 mg/dL or higher indicates diabetes.

Oral Glucose Tolerance Test (OGTT)

This blood glucose test, administered after fasting for at least eight hours, is performed two hours after drinking a glucose-containing beverage. It is also common to test blood prior to the glucose drink and then every 30 to 60 minutes afterwards for up to three hours. Both diabetes and prediabetes can be diagnosed this way, and it is routinely used to screen for gestational diabetes. A blood glucose level of 200 mg/dL or higher (two hours after drinking a beverage containing 75 grams of glucose) indicates diabetes. Because glucose levels are normally lower during pregnancy, gestational diabetes is based on slightly different numbers: 155 mg/dL two hours after drinking the glucose beverage.