University of Illinois Extension
 

How is diabetes diagnosed?

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There are several types of tests that can be used to diagnose diabetes or pre-diabetes: a Fasting Plasma Glucose Test (FPG), an Oral Glucose Tolerance Test (OGTT), a random non-fasting plasma glucose test, and a hemoglobin A1c test. Any test should beon at least two occasions.

According to the American Diabetes Association, a FPG test that results in a fasting blood glucose level between 100 and 125 mg/dl signals pre-diabetes. A person with a fasting blood glucose level of 126 mg/dl or higher has diabetes.

In the OGTT, a person's blood glucose level is measured after a fast and two hours after drinking a glucose-rich beverage. If the two-hour blood glucose level is between 140 and 199 mg/dl, the person tested has pre-diabetes. If the two-hour blood glucose level is 200 mg/dl or higher, the person tested has diabetes.

A random, non-fasting blood glucose of 200mg/dL or higher may indicate diabetes. Symptoms of increased urination, increase thirst, and unexplained weight loss would support a diagonsis of diabetes. The random test is usually followed by either FPG or OGT for confirmation.

The hemoglobin A1c test measures the level of glucose in your blood for the past three months. Two hemglobin A1c values greater than 6.5% would diagnose diabetes. If one value is above 6.5% and one is below 6.5%, a FBG or OGT is usually ordered by the doctor. Having values between 5.7% and 6.4% is pre-diabetes.

Back to: General Overview of Diabetes and Food

This document is a source of information only, and is not medical advice.