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A1c is Changing to Average Mean Blood Glucose

Posted: Wednesday, June 11, 2008

A1C Translation to Estimated Average Glucose (eAG) Units Will Yield Easier Patient Education. New more accurate formula used to convert A1c to average blood glucose.

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 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 cochair 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, 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 "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.

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.

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 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.

To convert an A1c to the new average mean blood glucose, use this formula:
eAG(mg/dl) = (28.7 X HbA1c) � 46.7

So the old method has an A1c of 6% at an average blood glucose of 135mg/Dl, and using the new formula will give you 126mg/DL, and a 7% A1c now equals a eAG of 154mg/DL instead of 170mg/DL.

A1c	Average Blood Glucose mg/dL.	eAG (New) mg/dL
5%	100	97
6%	135	126
7%	170	154
8%	205	183
9%	240	212
10%	275	240
11%	310	269
12%	345	298