Why is my A1C high when my blood sugar levels are in my target range?

Results of an A1C test and a blood glucose check don't always match up. The A1C test measures your average blood sugar levels over a 120-day period (the lifespan of a red blood cell). But a blood glucose check measures your blood sugar at a single moment. If your blood sugar levels were high last week, and you adjusted your diabetes treatment plan so that your blood sugar returned to normal, the A1C result may still be high, because it includes the high blood sugar levels from the previous week.

The A1C test measures the percentage of glycated hemoglobin in your blood. Glycated hemoglobin is created when molecules of hemoglobin (the oxygen-carrying protein in your blood) attach to molecules of glucose (the sugar in your blood). The more sugar you have in your blood, the higher your percentage of glycated hemoglobin.

Your blood glucose levels are probably based on your premeal blood glucose levels. While this usually works well, it does not take into account the level of your blood glucose after you eat. It may be that your blood glucose is rising unexpectedly after your meal because you are either not taking enough insulin or not taking insulin far enough ahead of eating your meal. To see if this is the reason that your A1C is high, measure your blood glucose 2 hours after breakfast, lunch, and dinner for several days (in addition to your premeal blood glucose levels). Blood sugar that is more than 200 mg/dl 2 hours after a meal is too high. In addition, your blood glucose may be high throughout the night, when you are asleep. To find out, wake yourself up at 4:00 a.m. several times during the week to check your blood glucose. At 4:00 a.m., blood glucose that is higher than 150 mg/dl is too high. Continue to check your blood glucose 2 hours after meals and in the middle of the night once a month to be certain that you are not having unexpected high blood glucose levels at these times.