A hemoglobin A1c (HbA1c) test measures the amount of blood sugar (glucose) attached to hemoglobin. Hemoglobin is the part of your red blood cells that carries oxygen from your lungs to the rest of your body. An HbA1c test shows what the average amount of glucose attached to hemoglobin has been over the past three months. It’s a three-month average because that’s typically how long a red blood cell lives.
The hemoglobin A1c (glycated hemoglobin, glycosylated hemoglobin, HbA1c, or A1c) test is used to evaluate a person’s level of glucose control. The test shows an average of the blood sugar level over the past 90 days and represents a percentage. The test can also be used to diagnose diabetes.[1]
Hemoglobin is a protein only found in red blood cells. In fact, hemoglobin is what gives blood it’s bright red coloring. Since red blood cells live about an average of three months, the A1c test will reflect those red blood cells that are present in the bloodstream at the time of the test; this is why the A1c serves as an average of blood sugar control.
The main job of hemoglobin is to carry oxygen from the lungs to all the cells of the body. Hemoglobin becomes glycated or coated with glucose from the bloodstream. The amount of glucose that is present in the blood will attach to the hemoglobin protein, and increased glucose levels will reflect on the surface of the hemoglobin protein, thereby rendering a higher A1c level.[2]
HbA1C test; Glycated hemoglobin test; Glycohemoglobin test; Hemoglobin A1C; Diabetes – A1C; Diabetic – A1C
A1C is a lab test that shows the average level of blood sugar (glucose) over the previous 3 months. It shows how well you are controlling your diabetes.
Why do I need an HbA1c test?
The Centers for Disease Control (CDC) recommends that adults over the age of 45 get tested to screen for diabetes and prediabetes. If your results are normal, you should repeat the test every 3 years. If your results show you have prediabetes, you should get tested every 1-2 years. You should also talk to your health care provider about taking steps to reduce your risk of developing diabetes.
If you are under 45, you may need this test if you have certain risk factors. These include:
- Being overweight or obese
- High blood pressure
- History of heart disease
- Physical inactivity
Testing should be done every 3 years, and more frequently if your results show you have prediabetes.
You may also need an HbA1c test if you have symptoms of diabetes. These include:
- Increased thirst
- Increased urination
- Blurred vision
- Fatigue
What happens during an HbA1c test?
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.
How the Test is Performed
A blood sample is needed. Two methods are available:
- Blood drawn from a vein. This is done at a lab.
- Finger stick. This can be done in your health care provider’s office. Or you may be prescribed a kit that you can use at home.
How to Prepare for the Test
No special preparation is needed. The food you have recently eaten does not affect the A1C test, so you do not need to fast to prepare for this blood test.
How the Test will Feel
With a finger stick, you may feel slight pain.
With blood drawn from a vein, you may feel a slight pinch or some stinging when the needle is inserted. Afterward, there may be some throbbing or a slight bruise. This soon goes away.
Why the Test is Performed
Your provider may order this test if you have diabetes. It shows how well you are controlling your diabetes.
The test may also be used to screen for diabetes.
Ask your provider how often you should have your A1C level tested. Usually, testing every 3 or 6 months is recommended.
Interfering Factors
There are several conditions where the HbA1c test can produce inaccurate results. People diagnosed with sickle cell anemia, thalassemia, anemia, kidney failure, liver disease, or patients receiving blood transfusions can experience altered results due to the longevity of the red blood cell. HbA1c measurement in these patients must be interpreted with caution and should be confirmed with plasma glucose samples to diagnose diabetes.[10]
A falsely low HbA1c value can result from several conditions including high altitude, pregnancy, hemorrhage, blood transfusion, erythropoietin administration, iron supplementation, hemolytic anemia, chronic kidney failure, liver cirrhosis, alcoholism, folic acid deficiency, sickle cell anemia, and spherocytosis. Vitamin C supplementation can either increase or decrease the HbA1c level depending on the method used for its measurement.[15]
On the other end of the spectrum, a falsely high HbA1c can be due to a lack of available iron in the blood. This condition can result from iron deficiency anemia, infection-induced anemia, or tumor-induced anemia. Hemoglobinopathies such as thalassemia can also cause a falsely high HbA1c. Other causes of falsely high HbA1c levels include hypertriglyceridemia, organ transplantation, and hyperglycation in certain ethnic groups. Medications such as immunosuppressants and protease inhibitors can sometimes lead to a falsely high HbA1c.[10][7][11][12]
Normal Results
If your HbA1c levels are high, it may be a sign of diabetes, a chronic condition that can cause serious health problems, including heart disease, kidney disease, and nerve damage.
The following are the results when A1C is being used to diagnose diabetes:
- Normal (no diabetes): Less than 5.7%
- Pre-diabetes: 5.7% to 6.4%
- Diabetes: 6.5% or higher
If you have diabetes, you and your provider will discuss the correct range for you. For many people, the goal is to keep the level below 7%.
The test result may be incorrect in people with anemia, kidney disease, or certain blood disorders ( thalassemia ). Talk to your provider if you have any of these conditions. Certain medicines can also result in a false A1C level.
The examples above are common measurements for the results of these tests. Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.
The approximate mapping between HbA1c values given in DCCT percentage (%) and eAG (estimated average glucose) measurements is given by the following equation:[rx]
- eAG(mg/dl) = 28.7 × A1C − 46.7
eAG(mmol/l) = 1.59 × A1C − 2.59
Data in parentheses are 95% confidence intervals
| HbA1c | eAG | ||
|---|---|---|---|
| % | mmol/mol[rx] | mmol/L | mg/dL |
| 5 | 31 | 5.4 (4.2–6.7) | 97 (76–120) |
| 6 | 42 | 7.0 (5.5–8.5) | 126 (100–152) |
| 7 | 53 | 8.6 (6.8–10.3) | 154 (123–185) |
| 8 | 64 | 10.2 (8.1–12.1) | 183 (147–217) |
| 9 | 75 | 11.8 (9.4–13.9) | 212 (170–249) |
| 10 | 86 | 13.4 (10.7–15.7) | 240 (193–282) |
| 11 | 97 | 14.9 (12.0–17.5) | 269 (217–314) |
| 12 | 108 | 16.5 (13.3–19.3) | 298 (240–347) |
| 13 | 119 | 18.1 (15–21) | 326 (260–380) |
| 14 | 130 | 19.7 (16–23) | 355 (290–410) |
| 15 | 140 | 21.3 (17–25) | 384 (310–440) |
| 16 | 151 | 22.9 (19–26) | 413 (330–480) |
| 17 | 162 | 24.5 (20–28) | 441 (460–510) |
| 18 | 173 | 26.1 (21–30) | 470 (380–540) |
| 19 | 184 | 27.7 (23–32) | 499 (410–570) |
Normal, prediabetic, and diabetic range
The 2010 American Diabetes Association Standards of Medical Care in Diabetes added the =HbA1c ≥ 48 mmol/mol (≥6.5 DCCT %) as another criterion for the diagnosis of diabetes.[rx]
| HbA1C | Diagnosis |
|---|---|
| <5.7% | Normal |
| 5.7-6.4% | Prediabetes |
| >6.4% | Diabetes |
What Abnormal Results Mean
An abnormal result means that you have had a high blood sugar level over a period of weeks to months.
If your A1C is above 6.5% and you do not already have diabetes, you may be diagnosed with diabetes.
If your level is above 7% and you have diabetes, it often means that your blood sugar is not well controlled. You and your provider should determine your target A1C.
The higher your A1C, the higher the risk that you will develop problems such as:
- Eye disease
- Heart disease
- Kidney disease
- Nerve damage
- Stroke
If your A1C stays high, talk to your provider about how to best manage your blood sugar.
A1C and self-monitoring
A part of your treatment plan will include self-monitoring at home with a blood glucose meter or other device. Your health care team will direct you on how often and when you should test your blood sugar.
Your self-monitoring device reports your blood sugar levels in milligrams of sugar per deciliter (mg/dL) or millimoles of sugar per liter (mmol/L). The measurement shows your blood sugar level at the time you do the test. Therefore, there is some variability throughout the day based on eating, exercise, stress and other factors.
Self-monitoring helps you make choices about diet and exercise and daily treatment goals, but it also helps you track whether you are meeting your A1C target. For example, if your A1C target is below 7%, your self-monitoring blood sugar levels should be, on average, below 154 mg/dL (8.6 mmol/L).
A1C test results generally correspond with the following results of blood sugar levels:
| A1C level | Estimated average blood sugar (glucose) level |
|---|---|
| 6% | 126 mg/dL (7 mmol/L) |
| 7% | 154 mg/dL (8.6 mmol/L) |
| 8% | 183 mg/dL (10.2 mmol/L) |
| 9% | 212 mg/dL (11.8 mmol/L) |
| 10% | 240 mg/dL (13.4 mmol/L) |
| 11% | 269 mg/dL (14.9 mmol/L) |
| 12% | 298 mg/dL (16.5 mmol/L) |
Limitations of the A1C test
Some factors may interfere with the accuracy of A1C test results. These include:
- Pregnancy
- Recent or heavy blood loss
- Recent blood transfusion
- Conditions that result in insufficient red blood cells (anemias)
- Hemoglobin variants
The most common form of the oxygen-transporting hemoglobin protein is called hemoglobin A. The presence of other variants of the protein may result in inaccurate A1C test results. Hemoglobin variants are more common among people of African, Mediterranean or Southeast Asian descent.
If you have a hemoglobin variant, your test may need to be sent to a specialized lab or you may need a different test for diagnosis and monitoring of diabetes.
Risks
Obtaining a blood sample from some people may be more difficult than from others.
Other risks of having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Common Questions
-
How is it used?
The test for HbA1c shows how well your diabetes has been controlled over the last 2-3 months. Even though you may have some very high or very low blood glucose values, HbA1c will give a picture of the average level of glucose in your blood over that time period. The result can help you and your doctor understand if the measures you are taking to control your diabetes are working.
In the past, the test was only used to monitor blood glucose control in patients with known diabetes. Now the World Health Organisation (WHO) recommends that HbA1c can also be used to diagnose type 2 diabetes in people who were not previously known to have the condition. There are certain situations in which HbA1c cannot be used to diagnose diabetes. An oral glucose tolerance test would be used as an alternative.
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When is it requested?
The Department of Health recommends that everyone with diabetes has HbA1c measured at least twice a year. HbA1c may be measured more frequently in those who have just been diagnosed with diabetes, in those whose blood glucose remains too high, or when a treatment plan changes. The test can also be used to diagnose type 2 diabetes. Please speak to your healthcare professional about local guidelines that may be in place, as there may be variations in local procedures., and there are certain groups of patients in which HbA1c cannot be used to diagnose diabetes.
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What does the test result mean?
If you have diabetes and your HbA1c is below 48 mmol/mol it is likely that your diabetes is well controlled. If your HbA1c rises above 48 mmol/mol, you are at increased risk of developing long-term complications such as eye disease, kidney disease, or nerve damage. It is worth noting that some people can find it difficult to get their HbA1c down to 48 mmol/mol without experiencing frequent episodes of hypoglycemia (low blood sugar), and if this is the case, the target HbA1c may be higher than 48 mmol/mol.
The World Health Organisation (WHO) suggests the following diagnostic guidelines for diabetes:
- HbA1c below 42 mmol/mol: Not diabetes
- HbA1c between 42 and 47 mmol/mol: Impaired glucose regulation or prediabetes.
- HbA1c of 48 mmol/mol or over: type 2 diabetes.
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Is there anything else I should know?
If you have an uncommon type of hemoglobin, known as a hemoglobin variant (for example thalassemia or sickle cell disease) , accurate results will depend on the method used to measure HbA1c. If you have hemolytic anemia or heavy bleeding, your test results may be falsely low. If you are iron deficient, this may raise your HbA1c result. HbA1c is not used for the diagnosis of diabetes during pregnancy.
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Is there a home test for HbA1c?
Yes. HbA1c could be measured at home but this is rarely done, is expensive, and should not be necessary if you are being monitored by your doctor.
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Are all HbA1c tests the same?
All HbA1c methods are now standardized to an IFCC reference material and are reported in mmol/mol standard units. Therefore, results generated by different laboratories are traceable to this global standard and comparable.
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