What is Glycated Hemoglobin?

Glycated hemoglobin is a modified form of hemoglobin that is present in the blood of most people. Checking its level in the blood relative to the level of normal hemoglobin is done to monitor patients with diabetes mellitus, and the value corresponds to the patients' average blood glucose levels over the past two months. Many doctors measure the glycated hemoglobin level and use the information in choosing a patient's diabetes treatment.

Hemoglobin is an oxygen-carrying molecule present in red blood cells. Each hemoglobin molecule is made of four polypeptide chains linked together by a number of chemical bonds. If the hemoglobin is exposed to an environment with high concentrations of oxygen, it can bind four molecules of oxygen. This oxygen is later released to peripheral tissues that need oxygen.

Glucose is the primary sugar the body uses for food. It can be obtained in the diet from foods rich in carbohyrates, or made from the breakdown of proteins and fats. Many tissues, including red blood cells and the brain, depend on obtaining glucose molecules from the blood to function properly.

Glucose molecules are able to enter red blood cells to serve as fuel. While in the cell, the glucose can bind to the end of one of the hemoglobin's polypeptide chains in a process called glycosylation. This reaction is officially called non-enzymatic glycosylation because the reaction proceeds without the help of a protein called an enzyme; in other circumstances, the enzyme would help to speed up chemical reactions. In normal patients, 5 percent of the total hemoglobin is glycosylated, or glycated, hemoglobin.

Patients with diabetes mellitus have high levels of glucose in their blood because of problems with the hormone insulin. Non-diabetics have a fasting blood glucose level of less than 100 micrograms per deciliter, whereas diabetics have a level of at least 126 micrograms per deciliter. The higher level of circulating glucose in patients with diabetes results in a larger amount of glucose entering red blood cells. More non-enzymatic glycosylation, and a higher glycated hemoglobin level, results.

Glycated hemoglobin is used clinically as a marker of the glucose levels patients have had in their blood. It is also called hemoglobin A1C, which is further abbreviated as HbA1C. The level reflects the average blood glucose level a patient had during the past two months because red blood cells, and therefore the hemoglobin contained in the red blood cells, have a half life of approximately 60 days. Checking the glycated hemoglobin offers a benefit over simply checking the blood glucose level, because it provides information about glucose control over an extended period; the blood glucose level only provides a snapshot of what the glucose level is at a given moment.

In diabetic patients, the glycated hemoglobin level is typically checked every three to six months. The goal for most patients is to have their glycated hemoglobin be less than 7 percent of their total hemoglobin, which corresponds to an average blood glucose level of approximately 154 micrograms per deciliter. Doctors often use the measurement as a way to pick a treatment plan for diabetic patients. Rising levels might indicate the need to add another diabetes medication to a patient's regimen.