Yesterday at Scientific Sessions there was interesting, even exciting news about a potential change in the A1C test. Most people with diabetes know that A1C is a measure of long-term glycemic control (glucose control). Although the test has been used for quite some time, not many people really understand what the value given with an A1C test (usually between 6 and 10%) really represents, or how that value is related to the numbers they get when they measure their blood glucose using a meter, which are much larger units and use a different scale altogether (usually 70 to 300 milligrams of glucose per deciliter, mg/dl). Those numbers make a certain amount of sense---we all know that having diabetes can mean higher levels of glucose on the bloodstream, and those levels can cause problems. But what's a "hemoglobin A1C"?
In this symposium, David Nathan from Harvard University provided the preliminary results from a clinical trial being performed to truly confirm that the A1C test reflects a patient's average blood glucose over the preceding 3 months. The data he showed, although preliminary, was very convincing. Although I suspect that most people think that that fact was established a long time ago, in fact the data supporting the idea that A1C exactly represents an average of a person's constant changes in blood glucose levels is pretty sketchy, and this clinical was needed to prove that that relationship exists.
As a result of this trial (when it's completed later this year), the A1C term and units will probably fade into the background, and taking its place will be the term "average glucose", and it will be expressed in the same units currently being used for diagnosis and self monitoring, mg/dl. You don't have to worry, however, that the test itself is changing, because laboratories will still do the A1C test, but rather than give people a confusing term with a confusing number, they'll just express a result as average glucose (which of course is what we think the A1C is). We'll just be expressing the results in terms that everyone is already familiar with. It was anticipated from the lectures that were presented that this change will take place starting in early 2008. Of course, nothing else is really going to change in that the test will still be performed, you'll just be given results that will be more easily understood.
There was also a lot of other discussion in the symposium about the calibration of the machines needed to do the A1C test, and in fact the test will be getting more accurate behind the scenes, but for people with diabetes the only difference they will see is a new name with new values. There was some discussion about what the term might be if we don't use the name "A1C", and the conclusion was that we would probably use the term "A1C-Derived Average Glucose", or ADA-G. If that change is made, expect to see a major effort by ADA and other groups to get the word out about ADA-G next year.