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EASD: Average Blood Glucose Will Replace A1c

Posted: Thursday, September 27, 2007

Because most patients do not understand what an A1c result means, the industry standard will now be to tell patients what their average blood glucose is.

What does a 6% A1c mean? Or a 9% A1c? Most patients do not correlate their A1c to an average blood glucose. So now, patients will be told what their Average Blood Glucose is. The A1c will still be available, but on their reports it will show there average blood sugar over the last 90 days.

But wait, the numbers are also going to change. An A1c of 6% was calibrated from the DCCT trials to be an average blood glucose of 135mg/dL and an A1c of 7% was equivalent to 170mg/dL. Because of the new technology of the continuous blood glucose monitors used in this study, they have come up with different numbers which are more accurate. What will the numbers be? We will have to wait until the end of the year when the study is published, before they give us the new numbers.

That's according to investigators who reported interim data from a study designed to determine whether an average glucose level, derived from HbA1c values, would accurately reflect what goes on day-to-day in patients' bloodstreams.

"These results are even better than we expected and that we could hope for," said Robert Heine, M.D., of the European Association for the Study of Diabetes (EASD), at the group's annual meeting here. Dr. Heine is also with the VU Medical Center in Amsterdam.

In August, the EASD, the American Diabetes Association, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), and the International Diabetes Federation released a consensus statement embracing a new standard for measuring and reporting HbA1c.

The groups also stated, conditionally, that "if the ongoing 'average plasma glucose' fulfills it's a priori specified criteria, an HbA1c-derived average glucose (ADAG) value calculated from the HbA1c result will also be reported as an interpretation of the HbA1c results."

When the reference standard changes were first announced, there was concern among physicians that patients would be confused by the new measurement, which would effectively change an HbA1c of less than 7% (the current ADA standard) from an "A" to a "C-," or as ADA President John Buse, M.D., put it, they'd be confused to find that "53 mmol/mol is the new 7%."

To prevent that confusion, the organizations agreed on a way to translate the new measurement into a uniform reference number: the IFCC reference number, expressed in mmol/mol, which can then be translated into the familiar current HbA1c values using simple mathematic formulas, and also into the more patient-friendly average blood glucose number.

The investigators then tested the accuracy of the average blood glucose number in an international study. David M. Nathan, M.D., of Harvard and Massachusetts General Hospital, the coordinating center for the trial, today chaired a session in which those updated results were announced.

Those results show that among 427 patients and healthy volunteers (each of whom had thousands of blood glucose monitoring results recorded over four months) there was at least a 90% correlation between the new reference standard and the average blood glucose level.

That's good news, because the average blood glucose number may be easier to grasp for patients who are accustomed to daily finger sticks and blood glucose monitoring anyway, Dr. Nathan said.

The International A1c-AG study was conducted at 10 centers in North America, Europe, and Africa, in an attempt to determine, as accurately as possible, the relationship between average blood glucose levels and HbA1c.

The study had recruited most of its goal of 700 volunteers, but one center had to drop out, because of technical problems. The investigators reported blood glucose data on 282 patients with type 1 diabetes, 140 with type 2, and 60 healthy volunteers with normal glycemia.

The patients' HbA1cs were measured in a central laboratory in the Netherlands using the new reference standard monthly for four months, with patients using a combination of continuous glucose monitoring for two to three days for each of the four months, plus frequent fingersticks equivalent to daily self-monitoring.

Using regression analysis, the investigators found that the standard error from the mean was only 0.83 mmol/mol, indicating that the average blood glucose measure correlated strongly with the new reference standard.

Dr. Nathan said that the relationship between HbA1c as measured by the new standard and average blood glucose appears to be the same for those with type 1 and type 2 disease, and for men and women.

The investigators expect to publish final results of the study later this year or in early 2008.

Practice Pearl: Explain to patients that in addition to receiving their current glycosylated hemoglobin levels, they may soon be able to receive reports of average blood glucose values that are similar to the readings they get during self-monitoring of blood glucose.

Source: Diabetes In Control: European Association for the Study of Diabetes Annual Meeting: "Monitoring of glycemia in people with diabetes: will mean blood glucose substitute HbA1c?" Presented Sept. 18