Hemoglobin carries oxygen within red blood cells. When blood sugar levels are high, the hemoglobin absorbs additional glucose, causing it to become glycosylated. A simple, non-fasting blood test, the hemoglobin A1c (glycosylated hemoglobin) level, can determine if glucose levels are consistently high over a period of weeks.
The glycosylated hemoglobin level is used to determine the average percentage of blood glucose levels over the approximate six weeks to three months before the test date. The hemoglobin A1c test is used along with daily blood glucose monitoring to determine whether a patient’s diabetes is adequately controlled.
A hemoglobin A1c level of approximately 5% is acceptable, with normal ranging from 4% to 5.6% indicated for non-diabetic individuals. In patients with a diagnosis of diabetes, the hemoglobin A1c is used to monitor glucose control while on medications over a period of weeks, in order to assess long-term success or failure of a medical treatment regimen consisting of injectable insulin and/or oral hypoglycemic agents, such as metformin or pioglitazone.
The hemoglobin A1c test was accepted as diagnostic for diabetes by the American Diabetes Association in 2010. A level of greater than 6% on a hemoglobin A1c is considered diagnostic of diabetes. Previously, fasting blood glucose levels or a glucose tolerance test were necessary for the diagnosis of diabetes, and some doctors still prefer to make the diagnosis based on a fasting blood glucose log over time.
Glycosylated hemoglobin levels are predictive of complications of high blood glucose levels over time. Complications of sustained high blood glucose levels may include neuropathy with numbness and tingling of extremities, vision problems, kidney dysfunction and poor healing of skin injuries or ulcerations.
Though it is reliably indicative of average blood sugar levels in most situations, some medical conditions can affect the glycosylated hemoglobin levels, including renal disease, liver dysfunction, or hypercholesterolemia. The levels may also be skewed by certain supplements and medications, so it is important that the patient list all medications being taken at the time of the test.
Because the hemoglobin A1c determines the average blood glucose levels over a long period of time, it is most often used to indicate the control of blood glucose in patients using diabetic medication. Adjustments to medical therapy and diet can be monitored over time using glycosylated hemoglobin levels. It is recommended that diabetic patients have their hemoglobin A1c level checked every 3 months. If levels are shown to be stable over time, the scheduled hemoglobin A1c checks may be reduced to twice a year.