Hemoglobin A1C testing: an introduction
Hemoglobin A1C testing (A1C) is the test used to measure your average blood glucose level over an extended period of time (2 to 3 months). It is used along with other blood glucose measurements, including random blood sugar testing, fasting blood sugar testing, and oral glucose tolerance testing, that provide a snapshot of your blood glucose at one point in time, to help determine whether your blood sugar is under control. The strength of A1C testing is that it is able to give a larger picture of how blood glucose levels change over days, weeks, and even months.
How does A1C testing work?
Hemoglobin is an important component of blood (it contains iron and gives blood its red color), responsible for transporting oxygen throughout the body. It is contained within red blood cells that have a lifespan of about 120 days.1
For the purposes of detecting elevated glucose levels and getting a picture of they change over time, hemoglobin A1C is useful because blood glucose tends to attach to hemoglobin. Normally, about 6% of hemoglobin has glucose attached. This combination of hemoglobin and glucose is called glycated hemoglobin or glycohemoglobin. There are different forms of glycohemoglobin, including A1A, A1B, and A1C. Of these, A1C is the most common, making up about two-thirds of glycohemoglobin.1
Advantages of A1C testing over glucose testing in diabetes
How is an A1C test done?
The A1C test is a blood test that your healthcare provider will perform. Someone at your doctor’s office or the clinic where you are having the test done will take a sample of your blood in the same way they do for any other blood test. The test is quick and there should be minimal discomfort. Some providers will send your blood off to a laboratory for analysis. Other providers have the laboratory equipment for analysis in the office (this is called point-of-care testing) and this allows them to get immediate results.
How is A1C testing used to diagnose or manage my diabetes?
A1C testing can be used by itself or in combination with the results of other blood glucose test results to diagnose diabetes or prediabetes. For the purposes of diagnosis, your healthcare provider will send your blood sample to a laboratory that uses a standardized and certified method of analysis or analyze the sample in the office if your provider has the equipment. An A1C result of 6.5% or above indicates diabetes.2,3
Hemoglobin A1C test results*
|Under 5.7%||5.7% to 6.4%||6.5% or above|
For diagnosis of diabetes, any test requires confirmation using a repeat measurement, unless symptoms of diabetes are clear.
A1C testing is also used to help manage your diabetes. Your healthcare provider may use an A1C test during your regular quarterly or semi-annual check-up to get a picture of your average blood glucose control over the past 2 to 3 months and to see if your diabetes treatment plan has been effective at helping you control your blood glucose.2,3
Are there limitations to A1C testing?
The strength of A1C testing is that it provides an accurate picture of blood glucose changes over time, as well as risk for certain complications. Results of A1C testing may be less reliable in people with certain health conditions. However, these conditions occur rarely.2 A1C results may be affected by abnormalities in rates of red blood cell survival. In some conditions, red blood cells may have a longer or shorter lifespan. A1C test results may also be affected if there is an abnormality affecting hemoglobin. Additionally, in chronic kidney disease, A1C measurements may be falsely increased or decreased. 1
How often should I have the A1C test?
A1C testing is useful in both screening and diagnosis of type 2 diabetes and in monitoring blood glucose control in people who have been diagnosed with type 2 diabetes. How often your healthcare provider will use A1C testing will depend on the purpose of the test (for screening or management).
Screening and diagnosis. The American Diabetes Association (ADA) recommends regular screening for type 2 diabetes in all adults age 45 and older who do not have prediabetes and/or other risk factors for type 2 diabetes every 3 years. For individuals who are overweight (body mass index [BMI] of 25 kg/m2 or greater) and have one additional risk factors that put them at increased risk for developing type 2 diabetes, testing should be done more frequently, for instance yearly for individuals with prediabetes (A1C 5.7% to 6.4%). The list of risk factors in addition to being overweight that warrants more frequent screening includes3,/sup>:
- Physical inactivity. Being physically inactive.
- Family history. Having a close family history of type 2 diabetes (a first degree relative with the disease).
- At risk ethnic group. Being in a high-risk ethnic group (eg, African American, Latino, Native American, Asian American, Pacific Islander).
- Gestational diabetes or baby with high birth weight. Being a women who delivered a high birth weight baby (more than 9 lbs) or was diagnosed with gestational diabetes.
- High blood pressure. Having high blood pressure (140/90 mmHg or greater) or being treated for high blood pressure.
- Abnormal lipids. Having an high-density lipoprotein (HDL) cholesterol level of 35 mg/dL or less or having a triglyceride level of greater than 250 mg/dL.
- Polycystic ovarian syndrome. Having polycystic ovarian syndrome.
- Prediabetes. Having prediabetes (impaired fasting glucose or impaired glucose tolerance or A1C of 5.7% to 6.4%).
- Cardiovascular disease. Having a history of cardiovascular disease.
- Insulin resistance. Other health conditions associated with insulin resistance (e.g., severe obesity).
Remember, if you have prediabetes (impaired fasting glucose or impaired glucose tolerance or A1C of 5.7% to 6.4%), this is a wake-up call to make healthy life changes to decrease your risk for developing type 2 diabetes, including losing weight (if you are overweight or obese) and getting regular moderate physical activity. Your healthcare provider may also decide that you might benefit from treatment with an oral diabetes medication that has been shown to prevent or delay the development of type 2 diabetes in people with prediabetes.
Management of type 2 diabetes. If you have been diagnosed with type 2 diabetes, regular A1C testing will play a role in monitoring how well your blood glucose is under control. The information that your healthcare provider gets from regular A1C testing will help him or her and you make adjustments to your care plan that will help you better control your blood sugar and reduce your risk for a range of diabetes-related complications.
The ADA recommends that A1C testing be performed at least 2 times a year in people who are achieving their treatment goals (keeping blood glucose under control). A1C testing should be done quarterly (every 3 months) in people whose treatment has recently been changed or who have not achieved their blood glucose treatment goal.
A1C targets. Your A1C treatment goal or target will depend to some degree on individual factors, including your age and health status. However, keeping A1C around or under 7% has been shown to decrease the risk of microvascular complications (these include complications where small blood vessels are affected, such as retinopathy and kidney disease). Keeping A1C levels under 7% is a reasonable goal for many non-pregnant adults. However, your healthcare provider may suggest an even lower A1C target of 6.5% or under, if you can achieve this goal without developing hypoglycemia or having side effects due to medication. Younger people who are diagnosed with type 2 diabetes sometimes use this lower A1C target. A higher A1C target of 8% or less may be appropriate for people who are affected by severe hypoglycemia, older people, or people with advanced cardiovascular disease, kidney disease, or other complications.3