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Estimated Average Glucose (eAG)

Diabetics may soon hear a new term and see new numbers that describe how well their disease is being controlled.

That term, “estimated average glucose (eAG),” refers to the result of a diabetic’s glycated hemoglobin (A1c) test, converted into an average blood glucose level in the units of measure seen on glucose meters. Both the American Diabetes Association (ADA) and the American Association for Clinical Chemistry (AACC) hope that using eAG helps patients and their doctors make the necessary changes to diet and physical activity to improve overall diabetes management.

While AACC has called upon laboratories to express A1c results as eAG, it favors a cautious approach to using this new term and number. In a recently released statement, AACC has asked labs to report eAG along with the A1c results patients are used to seeing. The basis of AACC’s position is what it identifies as the need for more data. “At the current time, there is inadequate data to justify sole reporting of eAG without the A1c result,” the statement notes. In particular, AACC calls for further study of whether it’s appropriate to use eAG in certain ethnic groups, pregnant women, and adolescents.

A1c tests, administered during doctor visits, measure average blood glucose control over the previous two to three months. With results stated in percentage points (i.e., A1c of 7%), A1c has long been an important tool in diabetes management. In general, A1c results indicate how successful a patient has been over a period of time in keeping glucose levels in a healthy range through daily self-testing and adjustments to insulin doses.

Diabetics test blood glucose levels several times a day, often before every meal. The readings from self-monitoring help patients fine-tune insulin doses to maintain their glucose levels within an acceptable range. These results are reported in different units than A1c, mg/dl (i.e., 170 mg/dl). Readings from self-monitoring represent the level of glucose in the blood at that moment in time, but do not give any indication of what glucose levels are at other times of day nor what average levels may be over several weeks as do results from the A1c test.

Like A1c, eAG evaluates a patient’s overall success at controlling glucose levels. However, by converting A1c percentage points to the same units as the meters patients use for daily self-monitoring (mg/dl), eAG results have the added advantage of giving physicians and patients a way to correlate A1c results to the daily readings, says ADA. With eAG, patients will see figures that differ greatly from the A1c results they have been receiving. For example, the usual A1c goal of 7% is the same as an eAG of 154 mg/dl. ADA hopes that using eAG will help patients better monitor their long-term glucose management.

A recent ADA recommendation that health professionals begin discussing eAG with patients in diabetes management education comes after a recent study, called ADAG for A1c-derived average glucose, showed a reliable correlation between A1c readings and average blood glucose levels. By comparing the measurement of A1c with the average glucose levels, study investigators were able to derive an equation allowing accurate interpretation of A1c levels as an eAG, according to ADA.

While eAG figures will help patients more directly see the difference between their individual meter readings and how they are doing with their glucose management overall, ADA notes that an eAG value is unlikely to match the average glucose level shown on a meter. That’s because diabetics are more likely to monitor their glucose first thing in the morning or before meals, when their blood glucose levels are low. So the average of these readings on glucose meters is likely to be lower than their eAG, which represents an average of their glucose levels 24 hours a day, including post-meal periods of higher blood glucose when people are less likely to test.
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