Critical Diabetes Test - A1C - Proven to be Accurate Average Glucose
San Francisco, California
June 7, 2008
A mathematical relationship between the average glucose level over the preceding three months and levels of the A1C test, thus yielding translation of the A1C for reporting as estimated average glucose (eAG), was proven in an international study published online today in the August issue of Diabetes Care. A1C has been used for more than 25 years as the major measure of glucose control and to establish targets for diabetes therapy.
"The findings of this large study have confirmed what smaller studies have shown and will give us confidence that A1C really does represent an average glucose because we now have a reliable formula to convert A1C into average glucose," said David M. Nathan, MD, Professor of Medicine, Harvard Medical School, and co-chair of the International A1C-Derived Average Glucose (ADAG) Study, in a recent interview. "While eAG will not replace A1C, physicians will be able to obtain reports both in A1C units of glycated hemoglobin and eAG units of milligrams per deciliter or millimols per liter, depending on the country, and choose which to use in clinical situations."
The implications of using eAG in mg/dl or mmol/L – the same units that patients use for self-monitoring of blood glucose (SMBG) at home – were discussed recently by his co-chair, Robert J. Heine, MD, PhD, Professor of Diabetology in the Department of Endocrinology at the VU University Medical Center in Amsterdam, Netherlands, and Executive Medical Director of the Diabetes and Endocrine Division of Eli Lilly and Company.
"It is extremely helpful for health care professionals and patients to be using the same language to discuss glucose goals," said Dr. Heine. "Since patients sometimes find it difficult to understand the concept of glycated hemoglobin, it will be much easier to have all test results -- both those from the lab and those the patient performs -- in the same units."
With A1C translated from a difficult-to-understand chemical entity into an easy-to-understand value that relates to the patient's every day home glucose monitoring, Dr. Heine predicts that eAG will prove to be a valuable education tool.
"When health care professionals set goals based on eAG units, then patients will know how close they are to reaching their goals every day when they test at home with self-monitoring,"said Dr. Heine.
Checking Blood Glucose Levels
People check their diabetes control at home by SMBG, usually by pricking their fingers for a blood sample and getting a reading using a simple monitor. Frequency varies depending on the type of diabetes and whether insulin injections are being used. Many people with type 1 diabetes, who must use insulin, do SMBG several times a day, or use continuous glucose monitors, which automatically check levels as often as every few minutes. The test provides information on blood glucose only at that moment.
In contrast, A1C testing is a measure of glucose control over the prior 2-3 months. The test measures the amount of glucose that has attached to a portion of the hemoglobin molecule in the blood. It is reported as the percent of hemoglobin molecules that has glucose attached. The American Diabetes Association recommends a goal of less than 7%. It is also known as glycated hemoglobin testing.
The International A1C-Derived Average Glucose Study
A group of international investigators conducted a 10-center study to try to define, as accurately as possible, the relationship between average blood glucose levels and A1C. The study recruited 507 volunteers of various races and ethnicities: 268 type 1, 152 type 2, and 80 without diabetes. The study measured A1Cs in a central laboratory monthly for 3 months, and measured average glucose levels using a combination of continuous glucose monitoring and frequent self-monitoring of blood glucose levels.
"We developed an equation that can be interpreted accurately as an estimated average glucose level by comparing the measurement of A1C with the average glucose levels,"explained Edward S. Horton, MD, Professor of Medicine, Harvard Medical School, and a co-author of the ADAG study, who will be presenting further information about the study at the American Diabetes Association's Scientific Sessions here tomorrow. Study investigators found a simple linear relationship.
"Although the tight and consistent relationship across different subgroups suggest that, for most people, there are no important factors that affect the relationship between A1C and average glucose, the study does have some limitations,"said Dr. Horton. In contrast to their intention and expectation, some ethnic-racial groups were under-represented, particularly people of African and Asian descent. Children and pregnant women were excluded from the study, as were patients who were not in stable control or with any suggestion of red blood cell disorders. So additional data in these groups would be needed to confirm the established relationship.
The American Diabetes Association (ADA), European Association for the Study of Diabetes (EASD), and International Diabetes Federation (IDF) will be working together to conduct educational efforts to make both patients and providers aware of this new terminology, and help to understand the relationship between A1C and AG. In the meantime, the American Diabetes Association announced that physicians can visit its Web site at www.diabetes.org to purchase a very inexpensive handheld calculator that will provide an instant conversion of A1C values to eAG.
Diabetes Care, published by the American Diabetes Association, is the leading peer-reviewed journal of clinical research into the nation’s fifth leading cause of death by disease. Diabetes also is a leading cause of heart disease and stroke, as well as the leading cause of adult blindness, kidney failure, and non-traumatic amputation. For more information about diabetes, visit the American Diabetes Association Web site at www.diabetes.org or call 1-800-DIABETES (1-800-342-2383).
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About the American Diabetes Association
More than 30 million Americans have diabetes, and every 21 seconds another person is diagnosed with diabetes. The American Diabetes Association (Association) is the global authority on diabetes and since 1940 has been committed to its mission to prevent and cure diabetes and to improve the lives of all people affected by diabetes. To tackle this global public health crisis, the Association drives discovery in research to treat, manage and prevent all types of diabetes, as well as to search for cures; raises voice to the urgency of the diabetes epidemic; and provides support and advocacy for people living with diabetes, those at risk of developing diabetes and the health care professionals who serve them. For more information, please call the American Diabetes Association at 1-800-DIABETESS (1-800-342-2383) or visit diabetes.org. Information from both of these sources is available in English and Spanish. Find us on Facebook (American Diabetes Association), Twitter (@AmDiabetesAssn) and Instagram (@AmDiabetesAssn)