People with diabetes will be familiar with finger-prick testing as a way to monitor how well diabetes is being managed. However, the A1C test can provide a longer-term picture of blood sugar levels.
A1C testing is essential for most people with diabetes.
This MNT Knowledge Center article explains the role this test plays in controlling blood sugar levels, as well as how it works.
- A1C measures glycated hemoglobin, which forms when glucose attaches to a protein in red blood cells.
- An initial diagnosis of diabetes is made if A1C levels are 6.5 percent or higher.
- Prediabetes, a risk factor for developing diabetes, is defined as A1C of between 5.7 and 6.4 percent.
- A result below 5.7 percent indicates a healthy blood sugar level.
- Results from A1C testing are easily converted into an equivalent blood glucose reading as given by home monitoring.
What is the A1C test?
The A1C blood test measures blood glucose over approximately 3 months.
The A1C test is a blood test used to measure the average level of glucose in the blood over a period spanning around 3 months.
This test is used to check how well blood sugar levels are being controlled in a person with diabetes and can also be used in the initial diagnosis of diabetes.
Hemoglobin is the protein in red blood cells (RBCs) responsible for transporting oxygen around the body. When blood glucose levels are elevated, some of the glucose binds to hemoglobin. RBCs typically have a lifespan of 120 days, and the A1C test offers an indication of longer-term blood glucose levels.
The type of hemoglobin to which glucose attaches is hemoglobin A, and the combined result is called glycated hemoglobin (A1C). As blood glucose levels rise, more A1C forms. This continues for about four months, which is the lifespan of an RBC.
The A1C level is directly linked to the average blood glucose level over the previous 12 or so weeks. A1C is a reliable test that has been refined and standardized using clinical trial data.
The blood test, performed at the doctor's clinic and sent for laboratory assessment, can be done at any time of the day and does not require special preparation. It is now also available as an instant result test available as some doctors' offices, known as a point-of-care test.
In January 2010, the American Diabetes Association (ADA) began recommending the A1C test began as a means of diagnosing and monitoring diabetes.
The World Health Organization (WHO) recommends the A1C test for diagnosis partly because of its convenience when compared to the two more traditional means of measuring plasma glucose levels that require a blood sample to be taken.
These are the fasting plasma glucose (FPG) test, which requires an 8-hour period beforehand in which the person being tested does not eat, and the oral glucose tolerance test, which takes place 2 hours after consuming a sweet drink.
In addition to its convenience, this test has become standard because it provides a measure of average glucose levels over the previous 12 weeks. In other tests, the result may be subject to the short-term variability of glucose levels.
The A1C test is at least as reliable at measuring glucose directly. The WHO and the ADA recommend a diagnosis of diabetes if a patient has an A1C of 6.5 percent or above.
However, diabetes is not automatically ruled out if a patient has an A1C lower than 6.5 percent.
A lower A1C value accompanied by a blood glucose level at any time of day of 200 mg/dl or above, or any clear signs of hyperglycemia, can also lead to a diagnosis of diabetes.
A diagnosis of prediabetes may be made in cases where A1C measures between 5.7 and 6.4 percent. This classification identifies people at increased risk of developing diabetes in the future.
Prediabetes is linked to obesity, high blood pressure, high cholesterol or triglycerides in the blood plasma, or low levels of high-density lipoproteins (HDL). Lifestyle and dietary changes will be recommended to try to address prediabetes and reduce the risk of diabetes in the future.
Reaching target glucose levels can help reduce the risk of complications and help a person maintain a good quality of life.
A normal blood glucose profile in someone without diagnosed diabetes is reflected by an A1C result below 5.7 percent.
When people have an A1C result of 6.5 percent or higher, they are diagnosed with diabetes., The treatment of diabetes aims to lower blood glucose and keep the A1C below 7 percent. Treatment usually involves lifestyle and dietary changes, oral medications, or insulin injections.
In general, the risk of complications from diabetes, such as cardiovascular disease, increases as A1C percentages rise.
Regarding prediabetes, using data from over 44,000 individuals in 16 cohort studies, and with an average follow-up time of 5.6 years, researchers determined that the risk of developing diabetes within 5 years is as follows:
- between 9 and 25 percent for those with an A1C of 5.5 to 6.0 percent
- between 25 and 50 percent for those with an A1C of 6.0 to 6.5
The relative risk of developing diabetes for people with an A1C of between 6.0 and 6.5 percent was 20 times higher than for those with an A1C of 5 percent.
For people with diabetes, the target A1C level is aimed at reducing the risk of complications related to damage to the small blood vessels, especially of the eyes and kidneys, including the coronary arteries.
Reaching and maintaining an A1C of 7 percent or lower significantly reduces these risks. This is the usual target set for people with diabetes, except for women who are pregnant.
It is recommended that some people with diabetes bring their A1C level even lower, less than 6.5 percent, as long as this does not lead to significant hypoglycemia or other adverse effects. This may be proposed for those with a shorter duration of diabetes, a long life expectancy, or no significant cardiovascular disease.
Other people may need less severe A1C goals, such as a target under 8 percent. This especially applies to people with diabetes and severe hypoglycemia, older adults, those not expected to live for many more years, and individuals with advanced diabetes complications.
When these targets have been difficult to reach despite optimal treatments, relaxing the A1C target may also be deemed appropriate in people with long-standing diabetes.
The A1C test result can be equated to the average of levels taken through the traditional self-monitoring of blood glucose.
The estimated average glucose (eAG) is a figure calculated from a number of directly measured blood glucose levels over time. It is expressed as milligrams per deciliter (mg/dl), similar to an individual reading obtained through home monitoring.
The ADA has produced a web-based converter to turn A1C readings into eAG readings and vice versa.
Doctors can use this reading to help make sense of the A1C reading for individuals accustomed to taking glucose measurements at home.
An A1C reading can be converted to an eAG reading as follows:
- 6.0 percent = 126 mg/dl
- 6.5 percent = 140 mg/dl
- 7.0 percent = 154 mg/dl
- 7.5 percent = 169 mg/dl
- 8.0 percent = 183 mg/dl
- 8.5 percent = 197 mg/dl
- 9.0 percent = 212 mg/dl
- 9.5 percent = 226 mg/dl
- 10.0 percent = 240 mg/dl
People should visit a doctor's office for A1C testing either quarterly or twice a year, depending on the stage of their diabetes.
A large study of A1C testing found that A1C testing once every three months can be ideal for helping people with diabetes maintain control over their blood glucose levels, especially those with a haemoglobin A1C of 7 percent or higher when first diagnosed.
The study, published in the journal Diabetes Care in 2014, found that testing A1C four times a year was associated with a 3.8 percent drop in A1C levels.
This improvement was in contrast to people who were tested just once a year. These people actually experienced a 1.5 percent rise in A1C levels. Also, compared to those tested just once a year, only half as many people in the group taking quarterly tests saw a significant rise in blood sugar levels.
The recommendations of the ADA, followed by healthcare providers in the United States, gives the following minimum standard for the frequency of A1C testing:
- at least twice a year for people who are meeting treatment goals and who have stable control over blood glucose levels
- quarterly for people whose treatment program changes or who are not meeting blood glucose goals
The guidelines also advise doctors to provide A1C testing in the office, providing an immediate opportunity to make appropriate changes to the treatment plan based on results that are instantly available.
A recent study in The Journal of Clinical Periodontology showed that good dental hygiene could help people with diabetes manage A1C levels.
In the wider field of diabetes testing, research in JAMA Internal Medicine discovered that self-monitoring blood glucose is only likely to benefit those undergoing insulin therapy.
Click here to keep up with all developments in diabetes diagnosis, monitoring, and treatment.