In light of the worldwide interest to develop a standardized assay for measuring glycated hemoglobin (HbA
1c) levels and the evidence of the prognostic significance of HbA
1c, the HbA
1c assay has been recommended by a subcommittee of the American Diabetes Association (ADA) to be adapted as a diagnostic tool for diabetes.
9 Earlier this year, the ADA added the HbA
1c assay to their criteria for the diagnosis of diabetes.
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According to this committee, whose members were appointed by the ADA, the European Association for the Study of Diabetes (EASD), and the International Diabetes Federation, a diagnosis of diabetes should be made when HbA1c levels are 6.5% or higher. The ADA recommends that the test be performed in a laboratory using a method that is certified by the National Glycohemoglobin Standardization Program and standardized to the Diabetes Control and Complications Trial assay. However, the HbA1c test may not be the single test, because of limited international standard, changes in glycation, certain ethnicities, age, abnormal hemoglobin, pregnancy, varying red blood cell turnovers, and renal disease.
According to the ADA, the criteria for diagnosing diabetes should be made when the patient has an HbA
1c of 6.5% or higher,
or a fasting plasma glucose (FPG) greater than 126 mg/dL,
or a 2-hour plasma glucose (PG) greater than 200 mg/dL during an oral glucose tolerance test (OGTT),
or, in a patient with classic symptoms of hyperglycemia or hyperglycemic crisis, a random plasma glucose level greater than 200 mg/dL.
10 In the absence of unequivocal hyperglycemia, the first three criteria should be confirmed by repeat testing. The categories for increased risk of diabetes are an HbA
1c level that is between 5.7% and 6.4%, an FPG level of 100 to 125 mg/dL, or a 2-hour PG level on the 75-g OGTT that is 140 to 199 mg/dL.
10 For all of these tests, the risk is continuous, becoming disproportionately greater at the higher ends of the ranges.
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