Also known as:
- Hemoglobin A1c
- Glycated Hemoglobin
- Glycosylated Hemoglobin
When first diagnosed with diabetes and then 2 to 4 times per year; as part of a health checkup or when you have symptoms of diabetes
When is it ordered?
Depending on the type of diabetes that a person has, how well their diabetes is controlled, and on doctor recommendations, the HbA1c test may be measured 3 to 4 times each year. The American Diabetes Association recommends A1c testing in diabetics at least twice a year (minimum). When someone is first diagnosed with diabetes or if control is not good, HbA1c may be ordered more frequently.
For diagnostic and screening purposes, A1c may be ordered as part of a health checkup or when someone is suspected of having diabetes because of signs or symptoms of increased blood glucose levels (hyperglycemia) such as:
- Increased thirst
- Increased urination
- Blurred vision
- Slow-healing infections
A blood sample drawn from a vein in your arm
Test Preparation Needed?
The HbA1c test evaluates the average amount of glucose in the blood over the last 2 to 3 months. It does this by measuring the concentration of glycated (also often called glycosylated) hemoglobin A1c.
Hemoglobin is an oxygen-transporting protein found inside red blood cells (RBCs). There are several types of normal hemoglobin, but the predominant form – about 95-98% – is hemoglobin A. As glucose circulates in the blood, some of it spontaneously binds to hemoglobin A. The hemoglobin molecules with attached glucose are called glycated hemoglobin. The higher the concentration of glucose in the blood, the more glycated hemoglobin is formed. Once the glucose binds to the hemoglobin, it remains there for the life of the red blood cell – normally about 120 days. The predominant form of glycated hemoglobin is referred to as HbA1c or A1c. A1c is produced on a daily basis and slowly cleared from the blood as older RBCs die and younger RBCs (with non-glycated hemoglobin) take their place.
This test is used to monitor treatment in someone who has been diagnosed with diabetes. It helps to evaluate how well their glucose levels have been controlled by treatment over time. This test may be used to screen for and diagnose diabetes or risk of developing diabetes. In 2010, clinical practice guidelines from the American Diabetes Association (ADA) stated that HbA1c may be added to fasting plasma glucose (FPG) and oral glucose tolerance test (OGTT) as an option for diabetes screening and diagnosis.
For monitoring purposes, an HbA1c of less than 7% indicates good glucose control and a lower risk of diabetic complications for the majority of diabetics. However, in 2012, the ADA and the European Association for the Study of Diabetes (EASD) issued a position statement recommending that the management of glucose control in type 2 diabetes be more “patient-centered.” Data from recent studies have shown that low blood sugar (hypoglycemia) can cause complications and that people with risk of severe hypoglycemia, underlying health conditions, complications, and a limited life expectancy do not necessarily benefit from having a stringent goal of less than 7% for their A1c. The statement recommends that people work closely with their doctor to select a goal that reflects each person’s individual health status and that balances risks and benefits.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
The A1c test is used to monitor the glucose control of diabetics over time. The goal of those with diabetes is to keep their blood glucose levels as close to normal as possible. This helps to minimize the complications caused by chronicallyelevated glucose levels, such as progressive damage to body organs like the kidneys, eyes, cardiovascular system, and nerves. The HbA1c test result gives a picture of the average amount of glucose in the blood over the last few months. This can help the diabetic person and his doctor know if the measures that are being taken to control his diabetes are successful or need to be adjusted.
HbA1c is frequently used to help newly diagnosed diabetics determine how elevated their uncontrolled blood glucose levels have been over the last 2-3 months. The test may be ordered several times while control is being achieved, and then several times a year to verify that good control is being maintained.
The HbA1c test may be used to screen for and diagnose diabetes. However, A1c should not be used for diagnosis in pregnant women, people who have had recent severe bleeding or blood transfusions, those with chronic kidney or liver disease, and people with blood disorders such as iron-deficiency anemia, vitamin B12 deficiency anemia, and somehemoglobin variants (e.g., patients with sickle cell disease or thalassemia). In these cases, a fasting plasma glucose ororal glucose tolerance test should be used for screening or diagnosing diabetes.
Only HbA1c tests that are NGSP Certified should be used for diagnostic or screening purposes. Currently, point-of-care tests, such as those that may be used at a doctor’s office or a patient’s bedside, are not accurate enough for use in diagnosis.
For monitoring glucose control,Hb A1c is currently reported as a percentage and, for most diabetics, it is recommended that they aim to keep their A1c below 7%. The closer diabetics can keep their A1c to the American Diabetes Association (ADA)’s therapeutic goal of less than 7% without experiencing excessive hypoglycemia, the better their diabetes is in control. As the HbA1c increases, so does the risk of complications.
An individual with type 2 diabetes, however, may have an HbA1c goal selected by the person and his doctor. The goal may depend on several factors, such as length of time since diagnosis, the presence of other diseases as well as diabetes complications (e.g., vision impairment or loss, kidney damage), risk of complications from low blood glucose (hypoglycemia), and whether or not the person has a support system and health care resources readily available. For example, a person with heart disease who has lived with type 2 diabetes for many years without diabetic complications may have a higher A1c target (e.g., 7.5%-8.0%) set by their doctor, while someone who is otherwise healthy and just diagnosed may have a lower target (e.g., 6.0%-6.5%) as long as low blood sugar is not a significant risk.
In screening and diagnosis, some results that may be seen include:
- A nondiabetic person will have an HbA1c result less than 6.3% (39 mmol/mol).
- Diabetes: HbA1c level is 6.5% (47 mmol/mol) or higher.
- Increased risk of developing diabetes in the future: A1c of 5.7% to 6.4% (39-46 mmol/mol)
The HbA1c test will not reflect temporary, acute blood glucose increases or decreases, or good control that has been achieved in the last 3-4 weeks. The glucose swings of someone who has “brittle” diabetes will also not be reflected in the HbA1c.
If an individual has a hemoglobin variant, such as sickle cell hemoglobin (hemoglobin S), they will have a decreased amount of hemoglobin A. This may limit the usefulness of the A1c test in diagnosing and/or monitoring this person’sdiabetes, depending on the method used.
If a person has had a recent blood transfusion, theHbA1c may be inaccurate and may not accurately reflect glucose control for 2 to 3 months.