For the last two decades, hemoglobin A1c has been a useful yet confusing concept. A measure of the proportion of blood hemoglobin to which sugar molecules have attached, the test is used to determine how well a diabetic patient has controlled his or her disease over the previous 6 to 8 weeks. Results are expressed as a percentage, with values less than 7.0% or 6.5% considered to be good diabetes control.
But this number doesn’t correspond in any visible way to what patients see when they test their blood sugar at home, which is expressed as a value in mg/dL. In general, 80-120 mg/dL is considered a “good number.” Now, a change in the international laboratory reference standard for measuring hemoglobin A1c has offered an opportunity to move away from the use of the confusing percentage to simply reporting hemoglobin A1c as an average blood sugar, expressed in the same units that patients see on their home glucose machines every day.
To my knowledge, my January 2007 article was the first by any journalist on this important clinical topic. In that and the two subsequent stories, I explained the issue to my physician readers, updated them on developments throughout the year, and prepared them for a shift in thinking about how to discuss test results with their diabetic patients.