Prediabetes is diagnosed with one of two blood testsa fasting plasma glucose test or a two-hour oral glucose tolerance test (OGTT). The fasting plasma glucose 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. For an oral glucose tolerance test, a patient is given a drink of 75 grams of glucose, and a blood draw is taken two hours later.
The following lab values are the American Diabetes Association (ADA) practice guidelines for the diagnosis of prediabetes diagnosis:
- A fasting plasma glucose value between 100 to 125 mg/dl (5.56 - 6.94 mmol/l) or more (indicating impaired fasting glucose).
- An oral glucose tolerance test plasma glucose value between 140 to 199 mg/dl (7.78 - 11.06 mmol/l) at 2 hours post-glucose load (indicating impaired glucose tolerance).
- An A1C range of 5.7 - 6.4%.
The ADA recommends that men and women age 45 and older, especially those that are overweight (i.e., BMI of 25 or higher), be screened for prediabetes. Screening should also be considered in individuals younger than 45 if they are overweight and have one or more additional risk factors.
If testing is positive for prediabetes, a follow up test should be performed on a subsequent day to confirm the diagnosis. People with diagnosed prediabetes should receive regular retesting every one to two years to monitor for type 2 diabetes. Individuals with a normal screening result can be retested every three years.
Reviewed by Francine Kaufman, M.D., 04/08
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