At every visit, patients ask "how did I do?" or "what is the hb A1c result?" High blood pressure and pulse rates are recorded prior to learning the results of the hb A1c. Families are incredibly anxious that the hb A1c will (or will not) accurately reflect the past 3 to 4 months of blood sugar readings. Most view the hb A1c as a grade that determines just how well they have managed their diabetes control between visits. I often hold my breath, hoping that my young patient has improved his/her hb A1c, because the visit has the potential to be a "downer" if they have not.
Much has already been written about how the hb A1c helps us to determine diabetes control. The hb A1c (or glycosolated hemoglobin) is a reflection of the amount of glucose that adheres to the hemoglobin molecule. There is a direct correlation--the higher the blood glucose concentration, the higher the hb A1c. The hemoglobin molecule resides in the red blood cell circulating throughout the bloodstream. Because red blood cells turn over approximately every 90 days, the hemoglobin A1c reflects about 90 days of blood glucose concentrations, which is why we obtain a hb A1c at every 3 to 4 month visit.
Keep in mind that the hb A1c does not always reflect blood glucose control if a patient has a hemoglobin type that is not "A." Patients that have hemoglobinopathies or hemolytic anemias such as Sickle Cell Disease or Hb C disease have much lower than expected hb A1c due to rapid red blood cell turnover. Likewise, if patients receive frequent red blood cell transfusions, the hb A1c will not be accurate. Sometimes, we do not know why the hb A1c does not reflect the average blood glucose concentration. In cases wherein the hb A1c does not reflect blood sugar control based on blood glucose monitoring or a continuous blood glucose sensor, we obtain a glycosolated protein (ie. albumin) or fructosamine level, which measures about 2 to 4 weeks of blood glucose control and correlates to different measures of hb A1c. However, fructosamine levels may be inaccurate if a patient has low levels of blood proteins.
Soon, with changes in the treatment of diabetes, patients will actually understand what the hb A1c level signifies. In most adolescent and pediatric diabetes practices, the hb A1c level is fully explained. However, it would be more educational to relate the average blood sugar level to the hb A1c reported. This new system will eventually record the hb A1c along with eAG (estimated average blood glucose in mg/dL.
Hb A1c (%) eAG (mg/dL)