What Is the A1C Test?

What to expect when undergoing this test

Blood sample on microscopic slide
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The A1C test, also known as an HbA1C, hemoglobin A1c, glycated hemoglobin, or glycosylated hemoglobin test, is a blood test that shows your average blood sugar levels for the past two to three months. It's a broader test than conventional home glucose monitoring, which measures your blood sugar at any given moment. It's used to diagnose and monitor diabetes.

Purpose of Test

Hemoglobin A, a protein found inside red blood cells, carries oxygen throughout your body. When there's glucose in your bloodstream, it can stick (glycate) to hemoglobin A. The more glucose that's in your blood, the more it does this, creating a higher percentage of glycated hemoglobin proteins.

Once glucose sticks to a hemoglobin protein, it typically remains there for the lifespan of the hemoglobin A protein (as long as 120 days). This means that, at any moment, the glucose attached to the hemoglobin A protein reflects the level of your blood sugar over the last two to three months.

The A1C test measures how much glucose is actually stuck to hemoglobin A, or more specifically, what percent of hemoglobin proteins are glycated. Hemoglobin with glucose attached to it is called A1C. Thus, having a 7 percent A1C means that 7 percent of your hemoglobin proteins are glycated.

Your doctor may order an A1C test for these reasons:

Screening for Diabetes

If you're overweight or obese and you have one or more other risk factors for developing type 2 diabetes, your doctor will likely order an A1C test as part of your normal medical exam every year. Such risk factors include:

  • A parent or sibling with diabetes
  • Being physically inactive
  • High blood pressure
  • Polycystic ovary syndrome (PCOS)
  • High triglycerides
  • Low HDL cholesterol
  • A history of heart disease
  • High-risk ethnicity (Native American, African American, Latino, Asian American)

The majority of people who end up with type 2 diabetes have prediabetes first, which means that your blood sugar is higher than normal, but not high enough to be diagnosed with diabetes. The A1C test can help monitor prediabetes.

The American Diabetes Association (ADA) also recommends that everyone age 45 years and older have the A1C test, regardless of other risk factors, because age itself is a major risk factor. If your test results are normal, you should have the A1C at least every three years. If you were diagnosed with gestational diabetes (diabetes while pregnant) that resolved after you had your baby, you will need to be tested at least every three years for the rest of your life as well.

The A1C test can be used to screen high-risk pregnant women for undiagnosed diabetes too, but only in the first trimester. During the second and third trimesters, diabetes needs to be screened with a glucose challenge test instead.

Diagnosing Diabetes

If you have symptoms like needing to urinate more often, feeling excessively thirsty and drinking more than normal, an increase in appetite, fatigue, infections that heal slowly, and/or blurry vision, your doctor may order an A1C test to check you for diabetes.

She may also order a random plasma glucose test, which measures your blood sugar level when your blood is taken, at the same time if you have these symptoms.

The ADA recommends that people who have symptoms of acute-onset type 1 diabetes, such as those listed above, have a plasma blood glucose test instead of the A1C for diagnosis. However, some doctors may do an A1C test as well to see how long blood sugar has been high.

Monitoring Diabetes

If you've been diagnosed with type 1 or type 2 diabetes, you'll periodically have an A1C test to monitor how well your diabetes is controlled and how your treatment is working.

How often you have it will depend on what type of diabetes you have, how controlled it is, and what your doctor recommends, but it will likely be two to four times a year.

Limitations

There are conditions in which the A1C test is not a reliable source for diagnosing diabetes, including sickle cell anemia, thalassemia, the second and third trimesters of pregnancy, anemia, hemolysis, iron deficiency, recently losing a lot of blood and/or having a blood transfusion, or undergoing erythropoietin therapy. These conditions can cause skewed results that don't reflect the reality of your blood sugar level. If you have one of these conditions, a fasting plasma glucose test is used for diagnosis instead.

Additionally, the A1C test needs to be done using methods that are certified by the NGSP and standardized to the Diabetes Control and Complications Trial (DCCT) analysis requirements in order to be as accurate as possible.

Before the Test

Once your doctor recommends the A1C, he'll let you know if he's going to do a random plasma glucose test at the same time. If you have questions about what your doctor is looking for or what's going to happen, this is the time to ask.

Timing

The blood test typically takes less than five minutes once the technician is ready to draw your blood.

Location

You may have this blood test right in your doctor's office or at a local hospital or lab.

What to Wear

Short sleeves are helpful, but not necessary, in case the technician needs to perform a blood draw. You can always just push or roll your shirt sleeve up.

Food and Drink

There are no fasting requirements for this test, or for the random plasma glucose test, which means they can both be done at any time.

Cost and Health Insurance

The A1C test is fairly inexpensive. If you have health insurance, it should be covered as other lab tests are whether it's done to screen or diagnose you for diabetes or to monitor your diabetes. You may have to pay a co-pay or co-insurance. Contact your health insurance company if you have any questions or concerns.

What to Bring

You can bring something to pass the time in the event you end up waiting for a while to get your blood drawn. Have your insurance and identification cards handy as well.

Other Considerations

You may have heard of A1C tests you can do at home. While these can be helpful in managing your disease once you're diagnosed with diabetes, they are not recommended for screening or diagnosing it. Talk to your doctor about this if you have questions.

During the Test

A lab technician, often a nurse or a phlebotomist (a person who is specially trained to draw blood), will collect your blood sample for the test.

Pre-Test

You may need to fill out a form or two before the test, for example, to give consent for the test or to authorize billing your insurance. The receptionist or nurse will let you know.

Also, be sure to let the technician know if you have a history of feeling faint or actually fainting during medical procedures. This allows the technician to take precautions, such as having you lie down on a table as your test is performed.

Throughout the Test

An A1C test is done via a regular blood draw or with a small drop of blood that's obtained from pricking your finger with a lancet, depending on the purpose of the test. If your doctor is screening for or trying to rule out or diagnose diabetes, you will have your blood drawn from a vein in your arm and sent to a lab that uses the NGSP-certified method.

For this process, you will need to roll or push up your sleeve, if applicable, on the arm you want the technician to use (most people choose their non-dominant arm). The technician will look for a vein—usually on the inside of your arm, in the crook of your elbow—and tie an elastic band around your arm above the vein to help push the blood down. After the area is cleaned with alcohol, a small, fine needle will be inserted into your vein. You will probably feel a sharp prick, pinch, or poke that lasts for just a few moments. Let the technician know if you start to feel faint, dizzy, or lightheaded.

Your blood will be collected in a tube and as it begins to fill up, the technician will untie the elastic band and then take the needle out of your arm. If the area is bleeding, a cotton ball or tissue will be pressed over it for a few seconds. If this doesn't stop the bleeding, the technician will place a bandage over the area.

If you're having an A1C test to monitor your diabetes after you've already been diagnosed, you'll probably have your finger pricked instead of the blood draw and the results will be determined right there at your doctor's office or lab. This is called a point-of-care test. It's a quick process that's mildly uncomfortable, but usually not painful, and one you will more than likely be used to at this point from testing your blood sugar levels at home.

Post-Test

As long as you aren't feeling nauseous or faint, you will be free to leave as soon as your blood sample has been taken. If you aren't feeling well, you may need to stay for a few minutes to recover first, but as soon as you are up to it, you can leave.

After the Test

Once your test is complete, you can go home and resume your normal activities.

Managing Side Effects

You may have some bruising, pain, or bleeding in the area in which your blood was drawn, but this should be mild and should only last for a few days. If it lasts longer or gets worse, call your doctor.

Interpreting Results

Depending on if your test was run in your doctor's office or sent off to a lab, your results may be ready the same day or it may take a few days or up to a week to get them back.

For diabetes screening and diagnosis, the reference ranges for A1C results are:

  • No diabetes: 5.6 percent or less
  • Borderline/prediabetes: 5.7 percent to 6.4 percent
  • Diabetes: 6.5 percent or higher

For monitoring diabetes control, experts disagree somewhat on what the A1C target should be. The ADA recommends a general A1C target of less than or equal to 7 percent, while the American Association of Clinical Endocrinologists (AACE) recommends a general target level of 6.5 percent or below. If you're diagnosed with diabetes, your doctor will discuss your A1C target with you.

Both the ADA and the AACE also emphasize that A1C goals should be individualized based on factors such as age, other medical conditions, length of time you've had diabetes, how well you comply with your treatment plan, and your risk of developing complications from hypoglycemia (low blood sugar). For example, if you have a reduced life expectancy; you've had diabetes for a long time and difficulty attaining a lower A1C goal; you have severe hypoglycemia; or you have advanced diabetes complications such as chronic kidney disease, nerve problems, or cardiovascular disease, your A1C target goal might be higher than 7 percent, but typically no higher than 8 percent. 

However, for most people, a lower A1C is ideal so long as they're not having frequent bouts of low blood sugar. Some people are able to substantially lessen their risk of complications from diabetes if they can keep their A1C under 7 percent. In general, the higher your A1C, the higher your risk of developing complications from diabetes.

Estimated average glucose: Some labs report your estimated average glucose (eAG), which is calculated from your A1C, along with your A1C result. Note that the A1C is not the same as the eAG, which is your two- to three-month average in mg/dL (milligrams per deciliter), the same measurement you use if you test your blood sugars daily. The eAG is designed to help you relate your A1C to your home glucose monitoring, though it won't be the same as your daily levels since it reflects an average over a few months.

Your A1c percentage can be translated into an estimated average blood sugar and vice versa.

28.7 X A1C - 46.7 = eAG

For example, an average blood glucose of 150 mg/dL translates into an A1C of about 7 percent. This is above normal, given that a diagnosis of diabetes is usually given when blood sugar levels reach about 126 mg/dL.

A1c to eAG Conversion Chart

HbA1c or A1ceAG
%mg/dlmmol/l
61267.0
6.51407.8
71548.6
7.51699.4
818310.1
8.519710.9
921211.8
9.522612.6
1024013.4

 

Most people have one type of hemoglobin: hemoglobin A. Some people of African, Mediterranean, or Southeast Asian heritage, or people who have family members with sickle cell anemia or a sickle cell trait, have hemoglobin A, as well as what's called a hemoglobin variant—a different type of hemoglobin.

Having a hemoglobin variant can affect the A1C test, making your blood sugar seem higher or lower than it actually is. Sometimes this hemoglobin variant becomes obvious when your blood glucose test or your home monitoring glucose tests don't match your A1C results, when your A1C result is extremely high, or if a recent A1C test is very different from the previous one.

 

 

Follow-Up

What happens next will depend on why you had the A1C test, as well as your results.

High A1C, but no symptoms of high blood sugar: If your A1C was high but you don't really have symptoms of high blood sugar, you may have another A1C test done, or your doctor may decide to do a fasting plasma glucose test (FPG) or a two-hour glucose tolerance test right away instead. In order to confirm the diagnosis of diabetes without the obvious symptoms of high blood sugar, two tests have to be abnormal, whether it's two A1C tests, two FPG tests, two two-hour tolerance tests, or one each of two of these tests.

Symptoms of high blood sugar and high A1C: If you do have symptoms of high blood sugar and your initial A1C is high, this will confirm a diabetes diagnosis, especially if you also had the random plasma glucose test done and that was high. This means that your doctor will need to see you as soon as possible to discuss starting a treatment plan to manage your diabetes. This plan will depend on whether you have type 1 or type 2 diabetes​, but may involve insulin supplementation, medication, glucose monitoring, exercise, and lifestyle changes.

Your doctor will likely repeat the A1C soon after you've started treatment to see how it's working and how well you're complying.

Borderline/prediabetes: If your A1C is borderline, your doctor will repeat this test on a yearly basis, as recommended by the ADA, to monitor your condition. He will likely also talk to you about lifestyle changes you can make that can help prevent diabetes.

Normal screening: If your doctor was screening you for diabetes because you have risk factors and your A1C was normal, you will need this test at least every three years. You may have it more often, depending on the initial results and your other risk factors. Your doctor will discuss how often you need this test with you.

Monitoring: In cases where you're having your A1C tested to monitor your diabetes, if it's within your target range, you may only need to have the test repeated twice a year. If it's higher than your target, your treatment plan may need some adjusting and your doctor will likely repeat the test sooner.

This test is recommended by the ADA at least twice a year for people whose diabetes is under control but may be done quarterly if you're newly diagnosed, your treatment plan has changed, or your diabetes isn't well-controlled.

Other Considerations

If your doctor suspects that you have a hemoglobin variant based on your A1C results, he will likely order a blood test to confirm it. If so, you can still have A1C tests done to monitor diabetes going forward, but they will need to be sent to a lab that uses a test that doesn't show interference from hemoglobin variants.

Talk to your doctor about any questions or concerns you have about your A1C test result and what your next steps are. If you're concerned about having a hemoglobin variant, ask your doctor about testing for this.

A Word From Verywell

Waiting for test results, especially when your doctor suspects that you have a chronic disease like diabetes, can be extremely anxiety-provoking. Make sure that you have an outlet for stress relief and that you're taking time to relax and unwind. Talk to a friend about your anxiety or work on learning some relaxation techniques like yoga, progressive muscle relaxation, or deep breathing. If you do end up with a diabetes diagnosis, keep in mind that treatments are better than ever and, with careful attention to your treatment plan and following your doctor's instructions to the letter, you can live your best life.

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