HbA1c is a widely used marker of chronic blood glucose levels, reflecting average values over a two to three month period. The test plays a critical role in the management of the patient with diabetes since it correlates well with both microvascular and, to a lesser extent, macrovascular complications. The HbA1c tests currently on the market are approved for monitoring a patient’s blood glucose control, but not for diagnosing diabetes.
For decades, the diagnosis of diabetes has been based on blood glucose tests, either the fasting plasma glucose or the 75-g oral glucose tolerance test. In a 2009 report, an International Expert Committee recommended the use of the HbA1c test to diagnose diabetes, with a threshold of ?6.5%, and the American Diabetes Association sustained this decision. They recommended a test certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized or traceable to the Diabetes Control and Complications Trial reference assay. However, HbA1c tests were not specifically designed or approved by FDA to be marketed for diabetes diagnosis, making it difficult to determine which HbA1c tests were accurate enough for this purpose.
The U.S. Food and Drug Administration, in May 2013, approved the marketing of the COBAS INTEGRA 800 Tina-quant HbA1cDx assay (Roche) for the diagnosis of diabetes by health care professionals. This is the first HbA1c test that the FDA has approved to be marketed for this use. In order to grant the approval, investigators analyzed 141 blood samples and found a less than six percent difference in the accuracy of test results from the Tina-quant HbA1cDx assay compared to results from the standard reference for hemoglobin analysis.
The Tina-quant HbA1cDx assay is a laboratory-based test. Health care providers can use it to both accurately diagnose diabetes and to monitor blood glucose control.
Advantages of using HbA1c to diagnose diabetes
HbA1c is a chronic marker of high blood glucose and it is already widely familiar to clinicians as a marker of glycemic control. Moreover, the HbA1C has several advantages to the fasting plasma glucose, including greater convenience since fasting is not required, evidence to suggest greater stability before the analysis and less day-to-day variations during acute stress and illness.
Disadvantages of using HbA1c to diagnose diabetes
There are some impediments in using the diagnostic HbA1c test including: a greater cost, a limited availability in certain regions of the developing world, and the incomplete correlation between HbA1C and the average glucose level in certain individuals. HbA1c tests, including the Tina-quant HbA1cDx assay, should not be used to diagnose diabetes during pregnancy and should not be used to monitor diabetes in patients with hemoglobinopathy, hereditary spherocytosis, malignancies, or severe chronic hepatic and renal disease. This test should not be used to diagnose or monitor diabetes in patients with the hemoglobin variant F.
Summary
Providing health care professionals with another tool to identify undiagnosed cases of diabetes should help them identify and manage people with diabetes before the complications appear.
References
1. FDA NEWS RELEASE: FDA allows marketing of first A1c test labeled for diagnosing diabetes, May 23 2013, http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm353653.htm
2. American Diabetes Association: Diagnosis and Classification of Diabetes Mellitus,
Diabetes Care, January 2013, 36:S67-S74; doi:10.2337/dc13-S067 http://care.diabetesjournals.org/content/36/Supplement_1/S67.full
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