A1C, also known as hemoglobin A1C is a simple lab test that reflects the body's average glucose levels over the past two to three months. It is determined by measuring the percentage of glycated hemoglobin in the blood and is the best measure of long-term diabetes control. Hemoglobin A1C is different from blood glucose level which measures the sugar level at one time only.
How it works
Hemoglobin is a protein in red blood cells that carry oxygen from the lungs to the cells of the body. When glucose is constantly elevated, as in uncontrolled diabetes, the excess glucose is bound to or "glycates" with hemoglobin in the bloodstream. The higher the glucose is in your blood on average, the higher the A1C levels becomes. Since the lifespan of a red blood cell is about 90 to 120 days, the amount of A1C in the blood reflects blood sugar control during the previous 90 to 120 days.
Importance of A1C
Many studies have looked at the relationship between A1C and the development of diabetes-related diseases like kidney and cardiovascular disease. According to the United Kingdom Prospective Diabetes Study, published in the August 2000 issue of the British Medical Journal, each one percent reduction in A1C was associated with a 14 percent reduction for myocardial infarction and a 37 percent reduction for microvascular complications. The lowest risk was being observed in those with A1C levels of less than six percent.
Frequency
The National Diabetes Information Clearinghouse recommend people with diabetes should have the A1C test at least twice a year. The health care team may check it more often--once every 3 months if the patient's blood glucose stays too high, and/or if there are treatment changes. The result will help your diabetes care team to determine whether further changes need to be made to your insulin regimen, diabetes medication, exercise and/or meal plan.
A!C Goal
For someone who does not have diabetes, A1C range is about five percent. The American Diabetes Association recommends that most people with diabetes maintain an A1C level at or below seven percent. A1C should be used in conjunction with self-monitored blood glucose data to make appropriate adjustment in diabetes care.
Limitations
A1C levels might vary significantly depending on the way the lab measures the level. Therefore it is important to look for the reference range the lab provides. A1C may be inaccurate in certain medical conditions including kidney failure, chronic excessive alcohol intake, acute or chronic blood loss, high triglyceride, sickle cell disease and gestational diabetes.
Expert Insight
According to a study published in the March 2010 issue of the New England Journal of Medicine, Selvin et al. demonstrated that A1C can be used to diagnose diabetes. The results showed that A1Cs were as effective as fasting blood glucose in identifying those who are at risk for diabetes. An advantage of A1C test over fasting glucose test in diagnosing type 2 diabetes is patients do not need to fast before testing, which will encourage more people to get tested.
References
- National Institute of Health. National Diabetes Education Program: The A1C Test: The Best Measure of Long-Term Diabetes Control. July 2005
- American Diabetes Association: Living with Diabetes: A1C.
- "British Medical Journal"; Association of Glycaemia with Macrovascular and Microvascular Complications of Type 2 diabetes: Prospective Observational Study; Stratton IM, Adler Al et al. Aug 12; 321(7258):405-12.
- "New England Journal of Medicine"; Glycated hemoglobin, diabetes...
