Insulin, secreted by the pancreas, controls blood glucose (sugar) levels by regulating production and storage of glucose from carbohydrates (starches and sugars) in the diet. With Type 1 diabetes mellitus, the pancreas produces little or no insulin, and diabetics must take insulin to control glucose. With Type 2 diabetes, diabetics may have decreased insulin or insulin resistance, which means the pancreas produces insulin but can't regulate glucose levels effectively. Blood glucose and (glycated) hemoglobin A1C are the two tests used to monitor glucose levels.
When glucose is absorbed into the bloodstream, some of it is picked up by the hemoglobin in red blood cells. This glycated (glucose-carrying) hemoglobin holds onto the glucose until the red blood cells die in about 120 days. The more glucose in the blood, the more glucose is carried by the hemoglobin--so a direct correlation exists between blood glucose level and glycated hemoglobin, which is measured to determine the A1C level.
Blood glucose monitoring reveals the level of glucose at a specific point in time. According to MedicineNet, normal blood glucose values range from 70 to 120 (before eating). Blood glucose levels may vary widely even in one day, depending on diet and exercise, but the A1C provides the average percentage of glycated hemoglobin in a 90-to-120-day period. Thus, both measurements are necessary to assess the success of treatment.
Red blood cells are continually being replaced. If the blood glucose level rises, hemoglobin picks up more glucose; if the glucose level falls, newer hemoglobin picks up less. Because red blood cells live for 120 days, the amount of glycated hemoglobin may vary in circulating red blood cells, but the average amount provides valuable information
According to MedicineNet, 4 percent A1C represents approximately 65 mg/dL of blood glucose, and each additional increase in percentage correlates to a 35-point increase in blood glucose. Normal A1C values are 4 to 5 percent. The American Diabetic Association recommends that diabetics maintain A1C below 7 percent, although others, such as the American Association of Clinical Endocrinologists, believe the A1C should be below 6.5, because maintaining a lower A1C prevents complications related to diabetes.
Type 1 Diabetics
Type 1 diabetics often check blood glucose levels one to four times daily with self-monitoring devices, because they need to determine if their insulin dosage is adequate. However, their blood glucose levels may vary widely, so they should also have an A1C about every three months to verify that their diabetes is well-controlled.
Type 2 Diabetics
Type 2 diabetics control the disease with diet, exercise and sometimes oral medications. Their glucose levels may vary between normal and elevated, so an isolated blood glucose level alone may not show their compliance with the treatment plan. The A1C test shows if they have been maintaining their glucose level within normal limits over a three-to-four-month period.