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Knowing your numbers: Hemoglobin A1C and blood glucose

If you have type 2 diabetes or are at risk for developing the disease, it is important to keep a close eye on your blood glucose levels (how much glucose is present in your blood).

With type 2 diabetes, body is unable to effectively use the insulin your body makes, due to insulin resistance and insufficient production of insulin. This leads to the uncontrolled blood glucose levels that characterize type 2 diabetes. If you’ve just been diagnosed with type 2 diabetes, chances are, the process that leads to diabetes has been developing for years. This means that you may already be affected by some of the common complications associated with diabetes, such as cardiovascular disease, nerve problems, and kidney disease. Other complications that can occur with type 2 diabetes include vision problems and problems with wounds healing on the feet.

Because type 2 diabetes is associated with a high risk for a variety of health complications, it is particularly important to have routine tests recommended by the American Diabetes Association (ADA) on a regular schedule to make sure that your blood glucose is controlled and to help identify health problems early and monitor existing problems as part of your diabetes care plan.1

Hemoglobin A1C (A1C) is one of the critical laboratory tests that you will have on a regular basis. Others include lipid testing (cholesterol and triglycerides), liver function testing, and blood pressure monitoring.

How does hemoglobin AC1 testing work?

Hemoglobin is an important protein component of blood (it contains iron and gives blood its red color), responsible for transporting oxygen throughout the body. It is contained within red blood cells that have a lifespan of about 120 days.2

Hemoglobin is useful for getting picture of blood glucose levels over time because blood glucose tends to attach to hemoglobin. Under normal circumstances hemoglobin that has glucose attached to it (called glycohemoglobin) makes up about 6% of hemoglobin. However, when there are high levels of glucose in the blood, this percentage increases. Therefore, measurement of glycohemoglobin (specifically hemoglobin A1C) is a good indicator of whether glucose levels have been higher than normal over a period of time. Because of the lifespan of red blood cells and because once glucose attaches to hemoglobin, it stays attached, measuring A1C gives us a good picture of blood glucose over a span of 8 to 12 weeks.2

While A1C testing does provide an accurate picture of blood glucose over time, results of A1C testing may be less reliable under certain conditions. A1C results can be affected by abnormalities in rates of red blood cell survival. In some conditions, red blood cells may have a longer or shorter lifespan. Test results can also be affected if there is an abnormality affecting hemoglobin. Additionally, in chronic kidney disease, A1C measurements can be falsely increased or decreased.2

Written by: Jonathan Simmons | Last reviewed: May 2014.
1. American Diabetes Association. Standards of Medical Care in Diabetes—2014. Diabetes Care 2014;37:S14-S80. -- 2. McCulloch DK. Estimation of blood glucose control in diabetes mellitus. Nathan DM, Wolfsdorf JI, Mulder JE, eds. UptoDate. Wolters Kluwer Health. Accessed at: 2013.