What Is an HbA1c Test?
An HbA1c test is a blood test that shows your average blood sugar (glucose) level over the past two to three months. It is also called a hemoglobin A1c, A1C, glycated hemoglobin or glycohemoglobin test. Health care professionals use it to screen for and diagnose prediabetes and type 2 diabetes. It is also the primary test used to manage diabetes.
A home glucose check shows your blood sugar at a single moment. An HbA1c test gives a longer-term picture, and you don't need to fast for it.
HbA1c Test at a Glance
| Also called | Hemoglobin A1c, A1C, glycated hemoglobin, glycosylated hemoglobin, glycohemoglobin |
|---|---|
| What it measures | The percentage of hemoglobin in red blood cells that has glucose attached |
| Time period reflected | About the past 2 to 3 months |
| Why it's ordered | To screen for or diagnose prediabetes and type 2 diabetes, and to monitor diabetes |
| Sample | Blood from a vein in the arm, or a finger stick |
| Fasting needed? | No |
| Results | Normal below 5.7%. Prediabetes 5.7% to 6.4%. Diabetes 6.5% or higher, confirmed by a second test unless there are clear symptoms. |
| Risks | Very little. Possible slight pain or bruising where the needle went in. |
What Does the HbA1c Test Measure?
Glucose in your blood sticks to hemoglobin, a protein in red blood cells. The higher your blood sugar, the more hemoglobin becomes coated with glucose. The test reports the share of coated hemoglobin as a percentage.
Glucose stays attached for as long as a red blood cell is alive, and red blood cells live about three months. That is why the result reflects a roughly three-month average. Blood sugar in the past 30 days has a greater effect on the result than blood sugar in earlier months. The test doesn't show sudden, temporary highs or lows.
Why Is an HbA1c Test Ordered?
Screening and diagnosis
Prediabetes and type 2 diabetes often cause no symptoms. Finding prediabetes early can help you prevent or delay type 2 diabetes.
- The CDC recommends A1C testing if you are over age 45.
- The CDC also recommends testing if you are younger, have overweight and have any other risk factor for prediabetes or type 2 diabetes.
- The US Preventive Services Task Force (USPSTF) recommends screening adults aged 35 to 70 who have overweight or obesity.
Other risk factors include a parent or sibling with type 2 diabetes, high blood pressure, past gestational diabetes and polycystic ovary syndrome (PCOS). Your provider may also order the test if you have symptoms such as feeling very thirsty, urinating a lot, blurred vision or losing weight without trying.
Monitoring diabetes
If you have diabetes, the test shows how well your treatment plan is working. Experts recommend an A1C test at least twice a year for people with diabetes, and more often if treatment goals aren't being met.
When the test isn't used for diagnosis
The A1C test should not be used to diagnose type 1 diabetes, gestational diabetes or cystic fibrosis-related diabetes.
How to Prepare for an HbA1c Test
No special preparation is needed, and you don't need to fast. Your provider may order other tests at the same time, such as cholesterol, that do require fasting.
Tell your provider about everything you take, because certain medicines, such as opioids and some HIV medicines, can affect results. Don't stop any medicine unless your provider tells you to. Also tell your provider if you are pregnant, since pregnancy may affect results. The blood draw usually takes less than five minutes.
For diagnosis, blood is drawn from a vein and sent to a lab that uses a method certified by the NGSP (formerly the National Glycohemoglobin Standardization Program). Point-of-care tests, which are analyzed in a doctor's office or clinic, should not be used for diagnosis.
What Do HbA1c Results Mean?
These ranges are used to diagnose prediabetes and diabetes:
| Result | HbA1c level |
|---|---|
| Normal | Below 5.7% |
| Prediabetes | 5.7% to 6.4% |
| Diabetes | 6.5% or higher |
Any test used to diagnose diabetes needs a second measurement to confirm it, unless there are clear symptoms. Within the prediabetes range, the higher the A1C, the greater the risk of diabetes. Results also vary slightly: a 6.8% result could read 6.4% to 7.2% on a repeat test of the same sample.
Estimated average glucose (eAG)
Some labs also report an estimated average glucose in mg/dL, the unit home meters use. The CDC lists these approximate matches:
| HbA1c | Estimated average glucose |
|---|---|
| 6% | 126 mg/dL |
| 7% | 154 mg/dL |
| 8% | 183 mg/dL |
| 9% | 212 mg/dL |
| 10% | 240 mg/dL |
The eAG won't match daily meter readings, because it is a long-term average.
HbA1c goals for people with diabetes
For most people with diabetes, the A1C goal is 7% or less. Your provider sets your personal goal based on your full medical history. Keeping A1C below 7% may not be safe for everyone, for example if it leads to low blood sugar (hypoglycemia). A goal between 7% and 8%, or sometimes higher, may suit people with limited life expectancy, long-standing diabetes and trouble reaching a lower goal, severe hypoglycemia or trouble sensing it, or advanced diabetes complications.
Goals matter because a higher A1C raises the risk of eye, heart, kidney and nerve problems and stroke. In a UK observational study of people with type 2 diabetes (UKPDS 35), each 1% lower average A1C was linked with a 21% lower risk of any diabetes-related complication or death and a 37% lower risk of small blood vessel (microvascular) complications.
What Can Affect HbA1c Accuracy?
Several factors can make an A1C result falsely high or low:
- Recent blood loss, a blood transfusion, sickle cell disease, hemodialysis or erythropoietin treatment
- Iron-deficiency anemia, which can falsely raise A1C
- Kidney failure or liver disease
- Certain medicines, including opioids and some HIV medicines
- Early or late pregnancy
- Inherited hemoglobin variants, most commonly hemoglobin S, C, D and E
Hemoglobin variants are more common in people with ancestors from Africa, South and Southeast Asia or the Mediterranean. Most people with a hemoglobin variant have no symptoms. Providers may suspect interference when A1C and blood glucose results don't match.
What Happens After Your HbA1c Result?
- Normal: your provider recommends a retesting schedule based on your age and risk factors.
- Prediabetes: you can take steps right away to prevent or delay type 2 diabetes, and your provider will likely repeat the test every 1 to 2 years.
- Diabetes: your provider discusses lifestyle changes and may prescribe medicine.
HbA1c Test vs. Other Blood Sugar Tests
| What it shows | Fasting? | Diabetes range | |
|---|---|---|---|
| HbA1c test | Average blood sugar over 2 to 3 months | No | 6.5% or higher |
| Fasting blood sugar test | Blood sugar after an overnight fast | Yes, at least 8 hours | 126 mg/dL or higher (prediabetes 100 to 125 mg/dL) |
| Oral glucose tolerance test | Blood sugar before and after a glucose drink | Yes | 200 mg/dL or higher at 2 hours (prediabetes 140 to 199 mg/dL) |
| Random blood sugar test | Blood sugar at the time of the test | No | 200 mg/dL or higher |
| Continuous glucose monitor (CGM) | Estimated glucose every few minutes, day and night, from a sensor under the skin | No | Not one of the CDC's listed diagnostic tests |
One test can show diabetes when another doesn't, so providers repeat testing before making a diagnosis. The A1C test also doesn't replace home monitoring, which shows how blood sugar changes through the day.
HbA1c Testing at GENEVA
At GENEVA Primary Care & Med Spa in Alpharetta, GA, a provider reviews your HbA1c result along with your symptoms, risk factors and other lab work. Based on that evaluation, your provider recommends next steps, which may include follow-up care at GENEVA or a referral to a specialist.
Ask about A1C testing during an annual physical exam, or as part of chronic disease management if you already have diabetes or prediabetes. GENEVA serves patients from Alpharetta, Johns Creek, Milton, Roswell and Cumming.
Related Terms
- Diabetes Screening
- Blood Sugar Monitoring
- Metabolic Panel (CMP/BMP)
- Lab Panels
- Preventive Screening
- Chronic Disease Management
- Anemia
- Body Mass Index (BMI)
- Insulin Resistance
HbA1c Test FAQs
What is a normal HbA1c level?
A normal HbA1c level is below 5.7%. A result of 5.7% to 6.4% is in the prediabetes range, and 6.5% or higher is in the diabetes range. Within the prediabetes range, the higher the number, the greater the risk of developing diabetes. A single high result usually isn't enough for a diagnosis. Unless there are clear symptoms, the result is confirmed with a repeat test on a different day, using A1C or another diabetes test. Ask your provider what your own result means.
Do you need to fast before an HbA1c test?
No, you don't need to fast before an HbA1c test. Food you have eaten recently doesn't affect the result, so blood can be drawn at any time of day. The draw usually takes less than five minutes. Tell your provider about all the medicines you take, because opioids and some HIV medicines can affect A1C results. Don't stop any medicine on your own, and mention if you are pregnant. If cholesterol or other fasting tests are ordered at the same visit, follow those instructions.
How often should you get an HbA1c test?
How often you need an HbA1c test depends on your last result. People with diabetes usually have it at least twice a year, and more often if they aren't meeting treatment goals. With prediabetes, retesting every 1 to 2 years is typical. After a normal result, your provider sets a schedule based on your age and risk factors. For screening, the CDC recommends A1C testing for adults over 45, and the USPSTF recommends screening adults aged 35 to 70 with overweight or obesity.
How long does it take to lower your HbA1c?
A lower HbA1c takes time to show, because the test reflects about the past 3 months of blood sugar. Large changes in blood sugar over the past month will show up in your A1C, and the past 30 days affect the reading more than earlier months. For prediabetes, losing 5% to 7% of your starting weight and getting at least 30 minutes of activity 5 days a week may prevent or delay type 2 diabetes. Some people with diabetes reach an A1C below 6.5% with lifestyle changes and medicine. That usually means good management, not that diabetes went away.
What is the difference between HbA1c and fasting blood sugar?
HbA1c shows your average blood sugar over about 3 months, while a fasting blood sugar test shows your level at one moment after not eating. The fasting test requires at least 8 hours without food. A fasting result of 100 to 125 mg/dL is in the prediabetes range, and 126 mg/dL or higher is in the diabetes range. HbA1c needs no fasting and is less affected by short-term changes from food, exercise, illness or stress. One test can show diabetes when the other doesn't, so providers repeat testing before diagnosing.
Can an HbA1c test be wrong?
Yes, an HbA1c result can be falsely high or low in some situations. Recent blood loss, a transfusion, sickle cell disease, hemodialysis and erythropoietin treatment can all shift results by changing red blood cell life span. Iron-deficiency anemia can falsely raise A1C. Kidney failure, liver disease, certain medicines and early or late pregnancy can also affect accuracy. Inherited hemoglobin variants, such as hemoglobin S, C, D and E, can interfere with some A1C tests. If your A1C doesn't match your glucose readings, your provider may use a different A1C method or another test, such as fructosamine.
Can a primary care provider order and interpret an HbA1c test?
Yes, a primary care provider can order an HbA1c test and explain what the result means. It is a simple blood test, and the USPSTF diabetes screening recommendation specifically covers adults seen in primary care. At GENEVA, a provider reviews your result along with your symptoms, risk factors and other lab work. Based on that evaluation, your provider recommends next steps, which may include follow-up care at GENEVA or a referral to a specialist. If you have symptoms such as extreme thirst, frequent urination or weight loss without trying, mention them when you book your visit.