By Tara Dairman | June 20, 2008 3:00 pm
If you’ve ever wondered how your HbA1c level relates to the numbers you get on your blood glucose meter, help may be on the way. A recent study has found a more accurate way to "translate" HbA1c results into average blood glucose levels. In the near future, therefore, doctors and labs may be reporting HbA1c test results both as a percentage (the old way) and as an "estimated average glucose" (or eAG) number.
The HbA1c test, which is a measure of blood glucose control over the previous 2-3 months, measures how much glucose is bound to hemoglobin in the blood. It is expressed as the percent of hemoglobin molecules that have glucose attached. Typically, people who do not have diabetes have an HbA1c value of less than 6%; the American Diabetes Association (ADA) recommends an HbA1c goal of less than 7% for people with diabetes in general and lower goals for some individuals.
Now, the “International A1C-Derived Average Glucose” (ADAG) study has found a simple mathematical formula that can “translate” HbA1c levels into an eAG level expressed in milligrams per deciliter (mg/dl), the same units that people use when they monitor their blood glucose at home. (It can also translate HbA1c into an eAG in millimoles per liter [mmol/l], the unit commonly used outside of the United States.) The study was presented on June 7 at the American Diabetes Association’s Scientific Sessions; it has been published online in Diabetes Care and will appear in print in the August issue of the journal.
The study took place in 10 centers and enrolled around 500 volunteers of various races and ethnicities. The volunteers consisted of 268 people with Type 1 diabetes, 152 people with Type 2 diabetes, and 80 people without diabetes. The researchers used a combination of continuous glucose monitoring and frequent blood glucose monitoring (seven times per day) to measure people’s average glucose levels; they also checked their HbA1c levels in a central laboratory for three months.
By comparing these results, the researchers were able to develop a mathematical equation that accurately converted HbA1c levels into average glucose levels. They found the calculation to be about 84% accurate in all the different subgroups studied. The researchers point out, however, that people of African and Asian descent were underrepresented in the study, and that some groups of people—children, pregnant women, people with red blood cell disorders, and people whose diabetes was not in stable control—were not included in the study.
Why is this new number necessary? The researchers believe that an average glucose level in the units that people already use for self-monitoring will be easier to understand and will make it easier for people and their doctors see how to adjust their treatment.
It may take a year or more before eAG values start to show up alongside HbA1c values on lab reports across the country; this is because new software will need to be disseminated and loaded into lab machines. In the meantime, though, there are a few ways that you or your doctor can convert your HbA1c level into an eAG value now:
28.7 x HbA1c – 46.7 = eAG (in mg/dl)
Will eAG replace HbA1c down the road? The researchers who conducted this study think that it may. However, the eAG is just a new way of interpreting the same information provided by the HbA1c, and HbA1c values will still be reported by labs for the foreseeable future.
For more information about interpreting your HbA1c level, see the article “H-B-A-1-C (What It Is and Why It Matters).”
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