Diabetes Control and the "Hb A1c"
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 (%)
Now that you know your hb A1c and estimated average glucose level, what does this really mean? Keep in mind that the hb A1c is the estimated average blood sugar during an approximate 3-month period (assuming that you have the most common form of hemoglobin or do not have hemolytic anemia). The hb A1c does not tell you anything about blood glucose variability. What does this mean? Blood glucose variability reflects those highs and lows, or your ups and downs (such as the height or nadir of sine waves). This is very important because the goal for blood sugar control is not only to have an excellent hb A1c but to also have less variability of blood sugars. In other words, you want less peaks and valleys. A normal pancreas keeps blood sugars in a tight range. The ideal goal is to have an average blood sugar less than 180 mg/dl (in our pediatric practice at CNMC) with a hb A1c of < 8% AND a decrease in the variability of blood sugars.
Achieving a hb A1c of 7 may be done in many ways. Obviously an average of 150 mg/dl of blood sugars ranging in 300s and 50s is not the best way due to the enormous variability of blood sugars. Your care team would rather see an average blood sugar of 150 and a hb A1c of 7 with blood sugars in a tighter range (less peaks and valleys). You will also feel better with blood sugars that are not all over the place. Your diabetes team will help you diagnose the issues related to highs and lows based on blood glucose monitoring and in many cases the employment of continuous glucose sensors. Based on this information, we can then adjust basal insulin (Lantus, Levemir, or basal rates with rapid acting insulin, such as apidra, humalog or novolog), insulin to carbohydrate ratios, and correction factors (insulin sensitivity factor). Bolusing insulin before meals and snacks also has been shown to decrease the variability of blood sugars. One may also relate how much rapid acting carbohydrate to treat a low to avoid super spikes in blood sugars based on the correction factor. For example, for some patients, 15 grams will raise the blood sugar 50 mg/dl. Therefore if one gives 45 grams of rapid acting carbohydrates to treat a blood sugar of 40 mg/dl, one might expect a blood sugar of 190 mg/dl in 20-30 minutes, which is too much carbohydrate
The hb A1c truly reflects blood sugar control (assuming, once again, no hemoglobinopathies or hemolytic disease). Therefore, if one fabricates blood sugars, the truth will be revealed…eventually. I highly recommend truthfulness in reporting blood sugars to avoid a dramatic office interaction. Most diabetes teams know about all the different methods used to avoid reporting truthful blood sugars. We are very effective detectives in this regard. Please work with your team to resolve problems in blood sugar management. We are here to help you achieve the best hb A1c possible in association with the least variability of blood sugars! And remember, the hb A1C is only one measurement in a sea of thousands of future hb A1Cs. There will be many opportunities for improvement with the help of your diabetes team!
Fran Cogen, M.D., C.D.E., is the director of the Childhood and Adolescent Diabetes Program at Children’s National Health System. She wrote about diabetes for HealthCentral.