Glycosylated hemoglobin

Glycosylated hemoglobin (also known as HbA1c) is a form of hemoglobin that is chemically linked to a sugar. Most monosaccharides, including glucose, galactose and fructose, spontaneously (i.e. non-enzymatically) bond with hemoglobin, when present in the bloodstream of humans. However, glucose is less likely to do so than galactose and fructose, so that hemoglobin A1c (HbA1c) is not a complete measure of glycemic control in diabetes mellitus.

Overview

The process of glycosylation of hemoglobin has been extensively studied and it is now known that the glycosylation process is irreversible. Once the glucose molecule is attached to the hemoglobin, it remains there for the life of the red blood cell. The amount of glycosylated hemoglobin is a long-term measure of average blood glucose levels over the previous 120 days (the lifespan of red blood cells).

Clinical Significance

In diabetes mellitus, higher amounts of glycosylated hemoglobin, indicating poorer control of blood glucose levels, have been associated with cardiovascular disease, nephropathy, and retinopathy. A trial on a group of patients with Type 1 diabetes found that monitoring glycosylated hemoglobin in subjects' blood decreased the risk of retinopathy and nephropathy.

Measurement

Glycosylated hemoglobin is typically measured to determine the three-month average plasma glucose concentration. The test is limited to a three-month average because the lifespan of a red blood cell is four months (120 days). However, since red blood cells do not all die at once, HbA1c is taken as a limited measure of three months.

See Also

• Hemoglobin
• Diabetes mellitus
• Glucose
• Nephropathy
• Retinopathy

Glycosylated hemoglobin Resources
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