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ADA: The Death of the A1c Test Results? Coming Soon Average Blood Glucose

After the first of the year, the A1c results will probably get reported to patients as an average blood glucose. Will this will help the 75% of diabetics who don’t know what an A1c test is? It might just make it even more confusing for the patient.

The preliminary results from an international study showing the relationship between hemoglobin A1c levels and average blood glucose levels, were reported yesterday at the American Diabetes Association's 67th Annual Scientific Sessions. Should the final results of the study replicate the early findings, doctors will likely report A1C test results in new average glucose (AG) units, so that patients will better understand the results of A1C testing.

In a 10-center study to try to define, as accurately as possible, the relationship between average blood glucose levels and A1C. The study has recruited almost 650 of its goal of 700 volunteers (300 type 1, 300 type 2, and 100 without diabetes) of various races and ethnicities. The study involves measuring their A1Cs in a central laboratory (in the Netherlands and using the new reference standard) monthly for 4 months, and measuring average glucose levels using a combination of continuous glucose monitoring and frequent finger-stick glucose levels equivalent to SMBG. "By comparing the measurement of A1C with the average glucose levels, we can derive an equation so that A1C levels can be interpreted accurately as an average glucose level or AG." said Dr. Nathan. No longer will a 6% be equal to 135mg/dl. Results from the study will give us new numbers and a formula to calculate the Average Blood Glucose.

"The reporting of A1C -- using that name -- in percentage units, such as a goal of under 7 percent, has always presented problems in doctor-patient communications," said David Nathan, MD, Professor of Medicine, Harvard Medical School, in a recent interview. "Yet this is the single most important assay in diabetes today because it assesses both chronic glucose control and risk for complications." He spoke at a symposium entitled, "Can 'Average Blood Glucose' Replace the A1C?"

The introduction of a new A1C calibration methodology by international authorities presented an opportunity to demonstrate that an A1C test result truly represents the average blood glucose value over the preceding few months. The International A1C-AG Study carefully compared A1C results to thousands of blood glucose values measured in each volunteer over a four-month period. "The ability of physicians to report A1C results to patients in the same units that they are using for self-monitoring -- so that they are using the same language to communicate glucose goals -- will certainly advance patient education," said Dr. Nathan.

The numbers people see when they test their blood sugars with a blood glucose monitor is a reading in milligrams per milliliter. So a reading after meal might be 125mg/dl. In contrast, A1C testing is a measure of glucose control over the prior few (2-3) months. The test is designed to measure the amount of glucose that has attached to a portion of the hemoglobin molecule in the blood. The assay is standardized on a reference method that takes into account a mixture of molecules. It is reported as the percent of hemoglobin molecules that has glucose attached.

With the introduction of the new reference method, an international consortium of investigators decided that it was an appropriate time to confirm that the A1C test truly does indicate the average blood glucose over time. Moreover, should the relationship be true, the investigators, under the auspices of the American Diabetes Association (ADA), European Association for the Study of Diabetes (EASD), and International Diabetes Federation (IDF), believe that a more easily interpretable A1C value for health care practitioners, and their patients, would be to express the test results as the "average glucose," and in units comparable to those obtained from self-monitoring.

The study is scheduled for completion by September 2007, with a final report to be presented at the annual EASD meeting in Amsterdam that same month.

By agreement between the IFCC and the ADA, EASD, and IDF, a plan is underway for the A1C tests to be reported in various ways:


With the current name and units, i.e. as A1C in percentages;

2. With the current name and in units that reflect the new reference method, i.e. as A1C in mmol/mol hemoglobin; and

3. Contingent upon success of the study, with a new name and new units,i.e. as ADAG (A1C derived average glucose) in mg/dl. or in mmol/lo dependent on the country. The addition of step 3 would take place after the results of the international study are analyzed in the fall of 2007 at the EASD meeting in Amsterdam. Presuming success, manufacturers of testing equipment will re-program their machines to print out all three values, and clinicians would be urged to use the ADAG term and units when reporting results to their patients.
Source: American Diabetes Association's 67th Annual Scientific Sessions, Chicago June 24, 2007
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