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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 carbohydrates, 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.
The hemoglobin A1c test -- also called HbA1c, glycated hemoglobin test, or glycohemoglobin -- is an important blood test used to determine how well your diabetes is being controlled. Hemoglobin A1c provides an average of your blood sugar control over a six to 12 week period and is used in conjunction with home blood sugar monitoring to make adjustments in your diabetes medicines.
Hemoglobin is a substance within red blood cells that carries oxygen throughout your body. When your diabetes is not controlled (meaning that your blood sugar is too high), sugar builds up in your blood and combines with your hemoglobin, becoming "glycated." Therefore, the average amount of sugar in your blood can be determined by measuring a hemoglobin A1c level. If your glucose levels have been high over recent weeks, your hemoglobin A1c test will be higher. The amount of hemoglobin A1c will reflect the last several weeks of blood sugar levels, typically encompassing a period of 120 days.
For people without diabetes, the normal range for the hemoglobin A1c test is between 4% and 6%. Because studies have repeatedly shown that out-of-control diabetes results in complications from the disease, the goal for people with diabetes is an hemoglobin A1c less than 7%. The higher the hemoglobin A1c, the higher the risks of developing complications related to diabetes.
People with diabetes should have this test every three months to determine whether their blood sugars have reached the target level of control. Those who have their diabetes under good control may be able to wait longer between the blood tests, but experts recommend checking at least 2 times a year.
Patients with diseases affecting hemoglobin such as anemia may get abnormal results with this test. Other abnormalities that can affect the results of the hemoglobin A1c include supplements such as vitamins C and E and high cholesterol levels. Kidney disease and liver disease may also affect the result of the hemoglobin A1c test.
The findings of the Diabetes Control and Complications Trial (DCCT) have conclusively shown that people with diabetes who manage their blood sugar well with A1c levels close to 7% can delay the onset or possibly even prevent diabetes-related complications that affect the eyes, kidneys and nerves. The DCCT showed that even an A1c of 8% significantly increased the risk of these complications.
The American Diabetes Association is now promoting a new term called estimated Average Glucose (eAG) that more accurately helps you convert your A1c test result into a number that corresponds to your glucose meter in mg/dl. For example, if your A1c test came back at 7.8%, that would convert to an estimated Average Glucose of 177 ml/dl. You can view a handy chart or do your own conversion of your A1c test result at their site.
You should have an A1c test performed immediately after diagnosis and then at least twice a year. Many endocrinologists recommend that those with type 1 diabetes have this test done every 3 months. That corresponds to the typical life span of red blood cells and gives you a continuous picture of your diabetes management.
The A1c test should be used in addition to your daily blood sugar testing. The A1c is only an average of what your blood sugar has been over the last three months. The only way you know for certain what your blood sugar level is at any given time is to test. So, it is still important that you test your blood several times each day for effective management.