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Type 2 Diabetes Diagnosis

Type 2 diabetes is often diagnosed in a doctor's office or other outpatient setting after chronic infection or other initial symptoms raise the suspicion of diabetes. Less frequently, a diagnosis is made in a hospital or emergency room after the extremely high blood glucose levels of undetected diabetes causes severe illness.

The National Institutes of Health (NIH) recommends that people age 45 and older consider getting tested for diabetes, and the American Diabetes Association (ADA) suggests a routine test every three years for those over 45, particularly if they are overweight, or for those under 45 if they are overweight and have another diabetes risk factor. Those with additional diabetes risk factors may require more frequent testing; talk to your doctor about the diabetes screening strategy that is right for you.

The preferred blood test for diagnosing type 2 diabetes is the fasting plasma glucose test. The test requires an eight-hour fast (no food or drink except water), after which a blood draw is performed. It is usually done in the morning. Other accepted tests for the diagnosis of type 2 diabetes include a random plasma glucose test (a blood draw taken at any time of the day) and an oral glucose tolerance test (OGTT; blood draws taken at intervals up to three hours after a patient consumes a drink of 75 grams of glucose).

The following lab values are the ADA practice guidelines for the diagnosis of diabetes:

• An A1C value of 6.5% or more
• A random plasma glucose value of 200 mg/dl (11.1 mmol/l) or more (in the presence of diabetes symptoms)
• A fasting plasma glucose value of 126 mg/dl (7 mmol/l) or more
• An oral glucose tolerance test with a plasma glucose value of 200 mg/dl or higher at 2 hours post-glucose load

The ADA also maintains that a definitive diabetes diagnosis requires a second positive test performed on a different day.

Reviewed by Francine Kaufman, MD. 4/08