The hemoglobin A1c test—also known as glycated hemoglobin, glycosylated hemoglobin, HbA1c, or simply A1c—is used to measure an individual’s glucose control levels. The test shows average blood sugar levels over the past 90 days, expressed as a percentage. In addition, it can be used to diagnose diabetes mellitus.[rx] Hemoglobin is a protein found exclusively in red blood cells, giving blood its bright red color. The primary role of hemoglobin is to carry oxygen from the lungs to all the cells in the body. Hemoglobin becomes glycated or coated with glucose from the bloodstream. As blood glucose levels increase, more glucose attaches to the hemoglobin protein, resulting in a higher A1c value.[rx] Since red blood cells have an average lifespan of about 3 months, the A1c test measures hemoglobin levels in the bloodstream over this period, making it a reliable indicator of blood sugar control.
Glycated hemoglobin, also called glycohemoglobin, is a form of hemoglobin (Hb) that is chemically linked to a sugar.[rx] Most monosaccharides, including glucose, galactose, and fructose, spontaneously (that is, non-enzymatically) bond with hemoglobin when they are present in the bloodstream. However, glucose is only 21% as likely to do so as galactose and 13% as likely to do so as fructose, which may explain why glucose is used as the primary metabolic fuel in humans.[rx][rx]
The formation of excess sugar-hemoglobin linkages indicates the presence of excessive sugar in the bloodstream and is an indicator of diabetes or other hormone diseases in high concentration (HbA1c > 6.4%).[rx] A1c is of particular interest because it is easy to detect. The process by which sugars attach to hemoglobin is called glycation and the reference system is based on HbA1c, defined as beta-N-1-deoxy fructosyl hemoglobin as a component.[rx]
Regular A1c testing is essential for individuals with diabetes mellitus to ensure their average blood glucose levels are within the target range. The American Diabetes Association (ADA) recommends that individuals with diabetes mellitus who have stable blood sugar control and are meeting treatment goals should have their HbA1c (A1C) checked at least twice a year.[rx] For individuals whose therapy has changed or who are not meeting glycemic targets, testing should be performed every 3 months. This approach helps optimize diabetes control and reduce the risk of complications.[rx]
Hemoglobin is made up of four protein chains called globins. Two of the globins are called alpha chains and two are called beta chains. Each globin has a compound with an iron molecule in the middle called a heme group. The iron molecule is what binds to oxygen to carry it through your body.
Mechanisms of Glycated Hemoglobin
Glycated hemoglobin causes an increase of highly reactive free radicals inside blood cells, altering the properties of their cell membranes. This leads to blood cell aggregation and increased blood viscosity, which results in impaired blood flow.[RX]
Another way glycated hemoglobin causes damage is via inflammation, which results in atherosclerotic plaque (atheroma) formation. Free-radical build-up promotes the excitation of Fe2+-hemoglobin through Fe3+-Hb into abnormal ferryl hemoglobin (Fe4+-Hb). Fe4+ is unstable and reacts with specific amino acids in hemoglobin to regain its Fe3+ oxidation state. Hemoglobin molecules clump together via cross-linking reactions, and these hemoglobin clumps (multimers) promote cell damage and the release of Fe4+-hemoglobin into the matrix of innermost layers (subendothelium) of arteries and veins. This results in increased permeability of interior surface (endothelium) of blood vessels and production of pro-inflammatory monocyte adhesion proteins, which promote macrophage accumulation in blood vessel surfaces, ultimately leading to harmful plaques in these vessels.[RX]
Highly glycated Hb-AGEs go through vascular smooth muscle layer and inactivate acetylcholine-induced endothelium-dependent relaxation, possibly through binding to nitric oxide (NO), preventing its normal function. NO is a potent vasodilator and also inhibits the formation of plaque-promoting LDLs (sometimes called “bad cholesterol”) oxidized form.[rx] This overall degradation of blood cells also releases heme from them. Loose heme can cause oxidation of endothelial and LDL proteins, which results in plaques.[rx]
Specimen Requirements and Procedure
The HbA1c test can be performed as a point-of-care (POC) test, a STAT test, or by sending a sample to a laboratory. The POC test uses a STAT analyzer to measure A1c from a capillary fingerstick. The laboratory test uses a teaspoon of blood drawn from a venous sample into a K2 EDTA (lavender top) tube. The sample is processed as whole blood. Patients do not have to fast for the HbA1c test, as it reflects long-term blood sugar control rather than immediate glucose levels.[rx]
Diagnostic Tests
The venous sample A1c test may be used as a diagnostic tool in clinical practice when determining diabetes risk or onset. Due to the variability of capillary POC testing, any A1c test conducted using a capillary sample should be confirmed with a venous sample before diagnosing. An HbA1c value below 5.7% is considered normal or non-diabetic. A value between 5.7% and 6.4% indicates prediabetes mellitus, whereas a 6.5% or higher level is diagnostic for diabetes mellitus. Tests should be sent to a laboratory certified by the NGSP to ensure standardized results.[rx][rx]
Why do I need an A1C test?
The Centers for Disease Control (CDC) recommends A1C testing for diabetes and prediabetes if:
- You are over age 45.
- If your results are normal, your provider will tell you how often you should be tested based on your age and risk factors.
- If your results show you have prediabetes, you will usually need to be tested every 1 to 2 years. Ask your provider how often to get tested and what you can do to reduce your risk of developing diabetes.
- If your results show you have diabetes, you should get an A1C test at least twice a year to monitor your condition and treatment.
- You are under 45 and are more likely to develop diabetes because you:
- Have prediabetes.
- Are overweight or have obesity.
- Have a parent or sibling with type 2 diabetes.
- Have high blood pressure or high cholesterol levels.
- Have heart disease or have had a stroke.
- Are physically active less than 3 times a week.
- Have had gestational diabetes (diabetes during pregnancy) or given birth to a baby over 9 pounds.
- Are African American, Hispanic or Latino, American Indian, or an Alaska Native person. Some Pacific Islander and Asian American people also have a higher risk of developing diabetes.
- Have polycystic ovarian syndrome (PCOS).
You may also need an A1C test if you have symptoms of diabetes, such as:
- Feeling very thirsty
- Urinating (peeing) a lot
- Losing weight without trying
- Feeling very hungry
- Blurred vision
- Numb or tingling hands or feet
- Fatigue
- Dry skin
- Sores that heal slowly
- Having more infections than usual
Testing Procedures
Numerous analytical techniques have been developed to quantify HbA1c, each offering specific advantages in precision and applicability. To ensure global consistency, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) established a reference system for HbA1c measurement. This system uses primary reference materials composed of purified HbA1c and HbA0, with 2 proposed reference methods—electrospray ionization mass spectrometry and capillary electrophoresis.[rx]
These reference methods target the glycated N-terminal valine of the hemoglobin β-chain. The process involves enzymatic digestion with endoproteinase Glu-C to release the N-terminal hexapeptide, followed by separation and quantification of glycated and non-glycated hexapeptides.[rx] HbA1c is expressed as the ratio of glycated to total hexapeptides. A network of IFCC-designated reference laboratories maintains and supports this standardized framework, ensuring its reliability for assay calibration.[rx]
Comparative analyses of the IFCC system with the NGSP and other regional standards demonstrate robust correlation, enabling manufacturers to align their assays with the IFCC reference method.[rx] However, HbA1c values derived from IFCC methods are typically 1.5% to 2% lower than NGSP values due to differences in the glycated fractions measured. The IFCC method is not intended for routine clinical use but is a calibration standard for commercial assays. For clinical testing, NGSP-certified methods are recommended.[rx]
In laboratory settings, high-performance liquid chromatography (HPLC) using cation-exchange chromatography remains a cornerstone technique for HbA1c measurement. This method effectively removes labile intermediates that may interfere with alternative approaches, such as immunoassays or affinity chromatography. Fully automated HPLC systems are widely available, requiring minimal sample volumes (approximately 5 μL of whole blood). Although venous blood is standard, capillary blood from a finger prick is also acceptable. Samples are diluted with a borate-containing hemolysis reagent and incubated at 37 °C for 30 minutes to eliminate labile Schiff bases before analysis.[rx][rx]
Immunoassay-based methods are also prevalent, using monoclonal antibodies that specifically bind to the Amadori product (ketoamine linkage) and distinct amino acid sequences at the N-terminal of the hemoglobin β-chain. A widely used format, latex agglutination inhibition, involves a synthetic polymer bearing HbA1c epitopes that competes with patient HbA1c for binding to antibody-coated latex beads. This competition reduces agglutination, which is quantifiable as decreased absorbance. Enzyme immunoassays using analogous antibodies exhibit acceptable precision and are typically calibrated to HPLC-derived values. These assays are highly specific, excluding labile intermediates; other glycated hemoglobin, such as HbA1a and HbA1b; and common hemoglobin variants, such as HbF, HbA2, HbS, and carbamylated hemoglobin.[rx][rx]
Recent advancements have introduced enzymatic assays using fructosyl peptide oxidase for HbA1c quantification, alongside automated liquid-flow capillary electrophoresis systems, which provide viable alternatives for routine clinical testing.[rx]
POC devices are increasingly used for HbA1c measurement in clinical settings. However, the diversity of available POC systems complicates selection, as comparative performance data are limited. Notably, POC measurements typically yield values approximately 0.5% lower than laboratory-based assays and may exhibit reduced accuracy compared to venous blood samples analyzed in a laboratory. Inter-laboratory variability in HbA1c results can reach 0.5%, underscoring the importance of standardized methodologies to ensure reliable clinical outcomes.[rx][rx]
How is A1C calculated?
A1C testing relies on hemoglobin. Hemoglobin is the part of the red blood cell that carries oxygen throughout your body. When you have glucose in your blood, it sticks to hemoglobin. This is called glycation. The more glucose is in your blood, the more it sticks. And it can stay there for around three months — about how long the average red blood cell lives.
The A1C test measures the average amount of glucose that’s been attached to hemoglobin over time. Because the A1C test measures glucose levels over a period of time, it provides more information about blood sugar than a single blood sugar test.
What should I expect during an A1C test?
You can expect the following during an A1C test that involves a sample from your vein, or a blood draw:
- You’ll sit in a chair, and a phlebotomist will check your arms for an easily accessible vein. This is usually in the inner part of your arm on the other side of your elbow.
- Once they’ve located a vein, they’ll clean and disinfect the area.
- They’ll then insert a small needle into your vein to take a blood sample. This may feel like a small pinch.
- After they insert the needle, a small amount of blood will collect in a test tube.
- Once they have enough blood to test, they’ll remove the needle and hold a cotton ball or gauze on the site to stop the bleeding.
- Finally, they’ll place a bandage over the site, and you’ll be finished.
You can expect the following during a finger prick A1C test:
- A healthcare provider will ask you which finger you’d like them to use.
- They’ll disinfect your fingertip with an alcohol swab and prick it with a small needle called a lancet, which is usually contained within a small plastic device.
- They’ll squeeze your fingertip to form a drop of blood and collect the drop in a small plastic container.
- After they have enough blood for the test, they’ll give you a cotton ball or gauze to hold against your fingertip to stop the bleeding.
- The results are usually ready within minutes.
What are the risks of an A1C test?
Blood tests are a very common and essential part of medical testing and screening. There’s very little risk to having either type of A1C test. You may have slight tenderness or a bruise at the site of the blood draw or finger prick, but this usually resolves quickly.
Results and Follow-Up
Mapping from A1c to estimated average glucose
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) |
HbA1C Test Normal Range
HbA1C test results are reported as a percentage, which represents the portion of your hemoglobin that is coated with sugar. Here’s how to interpret the numbers:
- normal : Below 5.7%
This corresponds to an average blood glucose level below 117 mg/dL or below 6.5 mmol/L. If your HbA1C falls within this range, it means your blood sugar is well controlled, and the risk of diabetes-related complications is low. - prediabetes : 5.7% to 6.4%
Prediabetes indicates that your average blood glucose level is between 117 and 137 mg/dL or 6.5 to 7.6 mmol/L. This range is a warning sign that requires immediate action, such as adopting a healthier lifestyle, to prevent diabetes. - Diabetes : 6.5% or higher
Diabetes is diagnosed when your HbA1C is 6.5% or higher, indicating an average blood glucose level of 140 mg/dL or higher, or 7.8 mmol/L and above. Effective management is important to reduce complications and improve health outcomes.
The normal range for HbA1C levels is below 5.7%. For individuals managing diabetes, the goal is often to maintain an HbA1C below 7%. However, this target may vary depending on age, overall health, and other personal factors. It is always important to consult with your doctor to determine the appropriate target for your situation.
Normal, prediabetic, and diabetic ranges
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]
| Diagnosis | “IFCC” HbA1c | “DCCT” HbA1c | “Mono S” HbA1c |
|---|---|---|---|
| Normal | < 40 mmol/mol | < 5.7% | < 4.7% |
| Prediabetes | 40–47 mmol/mol | 5.7–6.4% | 4.7–5.4% |
| Diabetes | ≥ 48 mmol/mol | ≥ 6.5% | > 5.5% |
What does my A1C mean?
An A1C test result is reported as a percentage. The number represents the portion of hemoglobin proteins that are glycated, or holding glucose. The higher the percentage, the higher your blood sugar levels have been over the last few months.
For diagnosing purposes, an A1C level of:
- Less than 5.7% means you don’t have diabetes.
- 5.7% to 6.4% signals prediabetes.
- 6.5% or higher usually indicates Type 2 diabetes (or Type 1 diabetes).
If you already have diabetes, an A1C result is a glimpse into how well your management plan has been working over the last three months. Management may involve oral pills, taking insulin, monitoring blood sugar levels and/or lifestyle changes, such as diet and exercise. Your A1C can help you and your provider determine if you should adjust any part of your treatment plan.
It’s important to remember that your A1C (if you have diabetes) is just an average measurement of your blood sugar over a few months. It’s not a grade or the ultimate determiner of whether you’re living a healthy life. Know that your A1C will change over your lifetime and that there are steps you can take to improve your diabetes management and A1C level, if needed.
A1C and estimated average glucose (eAG)
Some laboratories report your A1C results as a percentage in addition to the corresponding estimated average glucose (eAG).
The eAG calculation converts the A1C percentage to the same units you use with at-home glucose meters (glucometers) — milligrams per deciliter (mg/dL) or millimoles per liter (mmol/L). Just like your A1C is an average, the eAG is a single number that represents your average blood sugar level over the past three months.
For example, an A1C level of 7% equates to an eAG of 154 mg/dL (8.6 mmol/L). An A1C level of 9% equates to an eAG of 212 mg/dL (11.8 mmol/L).
What is a normal A1C?
For people without diabetes, a normal A1C is below 5.7%.
For people with diabetes, what’s “normal” and healthy for you depends on your goals and access to diabetes management medication and tools. Together, you and your healthcare provider will determine an A1C range that should be your target goal. This will likely change throughout your life.
In general, the American Diabetes Association recommends that the goal for most adults with diabetes should be an A1C of 7% or lower.
Your A1C goals may be above 7% if you have:
- Limited life expectancy.
- Severe low blood sugar (hypoglycemia) episodes or are unable to sense these episodes (hypoglycemia unawareness).
- Advanced diabetes complications, such as chronic kidney disease, nerve problems or cardiovascular disease.
On the other hand, healthcare providers typically recommend that people with Type 1 diabetes who are pregnant try to maintain an A1C of 6.5% or lower throughout their pregnancy. This is to try to lower potential health risks for the fetus and to try to prevent fetal macrosomia.
What is a dangerous level of A1C?
The higher your A1C levels, especially if they’re consistently high over several years, the more likely you’ll develop complications, such as:
- Retinopathy.
- Nephropathy.
- Neuropathy.
- Gastroparesis.
- Heart disease.
- Stroke.
Studies have shown that people with diabetes may be able to reduce the risk of diabetes complications by consistently keeping their A1C levels below 7%.
It’s important to remember that other factors can contribute to the development of diabetes complications, such as genetics and how long you’ve had diabetes.
Are A1C tests accurate?
Certain factors can affect the accuracy of A1C tests, including:
- Genetics, such as hemoglobin variants.
- Medical conditions.
- Medications and supplements.
- Errors in the collection, transport or processing of the test.
These factors can make your result falsely low or falsely high. Most of the factors are due to differences in the lifespan and health of your red blood cells.
Hemoglobin variants and A1C results
Hemoglobin variants can affect the results of some A1C tests.
The form of hemoglobin in your blood depends on the genes you inherit from your biological parents. There are many different forms. The most common form is hemoglobin A. Other, less common forms of hemoglobin are called hemoglobin variants.
A hemoglobin variant doesn’t increase your risk of developing diabetes, but it can affect A1C results. Labs have different ways to do A1C tests on blood with a hemoglobin variant.
The most common variants include:
- Hemoglobin C trait: Black people, people of West African descent and people from South and Central America, the Caribbean Islands and Europe are most likely to have this trait.
- Hemoglobin D trait: People who live in China, India, Turkey, Brazil and some parts of Europe are most likely to have this trait.
- Hemoglobin E trait: Asian Americans, especially those of Southeast Asian descent, are most likely to have this trait.
- Hemoglobin S trait: Black people and Hispanic Americans are most likely to have this trait.
A blood test can detect hemoglobin variants. Talk to your healthcare provider if you think you might have a hemoglobin variant that could affect your A1C results.
Causes of falsely low A1C results
The following conditions and situations can cause falsely low A1C results, meaning the result is lower than your actual A1C level:
- Alcohol use disorder.
- Blood transfusion.
- Chronic kidney failure.
- Erythropoietin-stimulating agents (ESAs).
- Hemorrhage (bleeding).
- Living at a high altitude.
- Iron supplementation.
- Cirrhosis of the liver.
- Pregnancy.
- Sickle cell anemia.
- Spherocytosis and hemolytic anemia.
Causes of falsely high A1C results
The following conditions and situations can cause falsely high A1C results, meaning the result is higher than your actual A1C level:
- Anemia, such as iron-deficiency anemia, infection-induced anemia or tumor-induced anemia.
- Certain medications, including immunosuppressant medications and protease inhibitors.
- Hypertriglyceridemia.
- Organ transplantation.
- Thalassemia.
- Vitamin B12 deficiency.
Can you have a high A1C and not have diabetes?
If you have an elevated A1C (above 6.5%) for the first time, it doesn’t always mean that you have diabetes. Other factors, such as certain medications (like steroids) or sickness can temporarily increase your blood sugar levels. Anemia and other conditions can cause a falsely high A1C result, as well. There also could’ve been an error in the collection, transport or processing of the test.
Healthcare providers rely on more than one test to diagnose diabetes. For example, they may order a fasting blood glucose test or another A1C test. In any case, your provider will carefully interpret your results and discuss them with you.
Is A1C an accurate representation of diabetes management?
For decades, healthcare providers and people with diabetes have relied on A1C as the main way to gauge how well their management of the condition is working.
For people with Type 1 diabetes, in particular, blood sugar can fluctuate significantly throughout the days, weeks and months. Because of this, A1C isn’t always an accurate measurement of management since it’s based on an average.
For example, a person who has frequent blood sugar fluctuations between significantly low and high episodes may have an A1C of 7%. A person who has blood sugar levels that stay more consistently around 154 mg/dL may also have an A1C of 7%.
More recently, with the invention of continuous glucose monitoring (CGM) devices, providers and people with diabetes have found time in range (TIR) to be a more helpful and accurate representation of diabetes management.
Time in range is the amount of time your blood sugar levels are in a recommended target range. TIR is measured as a percentage. Blood sugar range goals can vary for each person, but a typical target range is between 70 and 180 mg/dL. For most adults with Type 1 or Type 2 diabetes, providers recommend aiming to have a TIR above 70% (about 17 hours of a 24-hour day).
With CGMs and TIR, providers and people with diabetes can see how often they’re experiencing high or low blood sugar episodes. This can help them more accurately adjust treatment strategies.
Disclaimer: Each person’s journey is unique, treatment plan, life style, food habit, hormonal condition, immune system, chronic disease condition, geological location, weather and previous medical history is also unique. So always seek the best advice from a qualified medical professional or health care provider before trying any treatments to ensure to find out the best plan for you. This guide is for general information and educational purposes only. Regular check-ups and awareness can help to manage and prevent complications associated with these diseases conditions. If you or someone are suffering from this disease condition bookmark this website or share with someone who might find it useful! Boost your knowledge and stay ahead in your health journey. We always try to ensure that the content is regularly updated to reflect the latest medical research and treatment options. Thank you for giving your valuable time to read the article.
The article is written by Team RxHarun and reviewed by the Rx Editorial Board Members
Last Updated: November 06, 2025.
