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 chronically elevated glucose levels, such as progressive damage to body organs like the kidneys, eyes, cardiovascular system, and nerves. The A1c 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.
A1c 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.
Only A1c tests that have been referenced to an accepted laboratory method (standardized) 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 but can be used to monitor treatment (lifestyle and drug therapies).
Depending on the type of diabetes that a person has, how well their diabetes is controlled, and on doctor recommendations, the A1c test may be measured 2 to 4 times each year. The American Diabetes Association recommends A1c testing in diabetics at least twice a year. When someone is first diagnosed with diabetes or if control is not good, A1c 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:
For monitoring glucose control, 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 A1c increases, so does the risk of complications.
An individual with type 2 diabetes, however, may have an A1c 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.
The A1c test report also may include the result expressed in SI units (mmol/mol) and an estimated Average Glucose (eAG), which is a calculated result based on the A1c levels.
The purpose of reporting eAG is to help a person relate A1c results to everyday glucose monitoring levels and to laboratory glucose tests. The formula for eAG converts percentage A1c to units of mg/dL or mmol/L.
It should be noted that the eAG is still an evaluation of a person's glucose over the last couple of months. It will not match up exactly to any one daily glucose test result. The ADA has adopted this calculation and provides a calculator and information on the eAG on their DiabetesPro web site.
In screening and diagnosis, some results that may be seen include:
A nondiabetic person will have an A1c result less than 5.7% (39 mmol/mol).
Diabetes: A1c 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 A1c 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 A1c.
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's diabetes, depending on the method used.
If a person has anemia, hemolysis, or heavy bleeding, A1c test results may be falsely low. If someone is iron-deficient, the A1c level may be increased.
If a person has had a recent blood transfusion, the A1c may be inaccurate and may not accurately reflect glucose control for 2 to 3 months.
This article was last reviewed on November 30, 2012. | This article was last modified on December 29, 2014.
The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.
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