The hemoglobin A1c test — usually shortened to HbA1c, A1c, or glycated hemoglobin — is one of the most important blood tests in the diagnosis and management of diabetes. Unlike a single glucose measurement, which captures blood sugar only at the time of the blood draw, the A1c reflects the average blood glucose level over the previous two to three months.
This article explains what the A1c measures, what your result means, how it is used to diagnose and monitor diabetes, and what factors can affect its accuracy.
The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.
What is the hemoglobin A1c test?
Hemoglobin is the protein inside red blood cells that carries oxygen from the lungs to every tissue in the body. When glucose (sugar) is present in the blood, a small amount attaches to the hemoglobin molecule in a permanent way. This combined molecule is called hemoglobin A1c.
The percentage of your hemoglobin that is bound to glucose depends on how much glucose has been in your blood over the past two to three months. The higher your average blood sugar, the more hemoglobin gets glycated, and the higher your A1c. Because red blood cells live for about 120 days before being replaced, the A1c reflects the average glucose exposure over roughly that same time period — about three months.
This makes the A1c fundamentally different from a finger-prick or blood glucose test:
- A blood glucose test shows your blood sugar at the exact moment of measurement.
- The A1c shows your average blood sugar over the past two to three months.
For people with diabetes, the A1c is usually a more useful single test for long-term diabetes control because it isn’t affected by what you ate yesterday or whether you skipped a meal before the blood draw.
Why is an A1c test done?
The A1c is used in three main situations:
- To screen for and diagnose diabetes. The A1c is one of the standard tests for diagnosing type 2 diabetes and prediabetes in adults. It can be performed at any time of day and does not require fasting, which makes it more convenient than fasting glucose or oral glucose tolerance testing.
- To monitor diabetes over time. Once diabetes is diagnosed, the A1c is the primary tool for tracking how well blood sugar is being controlled. It is typically checked every three to six months.
- To assess risk in people without diabetes. A1c levels in the upper end of the normal range may indicate increased future risk of developing diabetes, even if they don’t yet meet the threshold for diagnosis. Many doctors use the A1c as part of a broader cardiovascular and metabolic risk assessment.
How is the test performed?
The A1c is performed on a small blood sample, usually drawn from a vein in the arm. No fasting is required, and the test can be done at any time of day, regardless of when you last ate. Some clinics now offer a finger-stick A1c test that provides results in a few minutes, though laboratory testing remains the gold standard, particularly when results are used to diagnose diabetes.
The result is reported as a percentage. Most laboratories also provide an estimated average glucose (eAG) alongside the percentage. The eAG converts the A1c into an estimated average glucose value in the same units used in finger-stick monitoring, making the result easier to relate to day-to-day glucose readings.
What does my A1c result mean?
The American Diabetes Association uses the following A1c thresholds for adults:
- Below 5.7% — normal. Reflects low average glucose levels and is consistent with the absence of diabetes or prediabetes.
- 5.7% to 6.4% — prediabetes. Indicates that average glucose levels are higher than normal, and the risk of progressing to type 2 diabetes is significantly increased. Lifestyle changes, weight loss, and increased activity can substantially reduce that risk.
- 6.5% or higher — meets the threshold for diabetes when confirmed by a repeat test. A single A1c result above 6.5% should be confirmed with a repeat test on a separate day or with another diagnostic test, such as fasting glucose or an oral glucose tolerance test.
For people who already have a confirmed diagnosis of diabetes, the A1c is interpreted differently. Rather than comparing to diagnostic thresholds, the goal is to evaluate how well treatment is working.
A1c targets for people with diabetes
Most adults with diabetes have a target A1c of below 7.0%. This target is associated with a substantially reduced risk of long-term complications, including:
- Diabetic eye disease (retinopathy)
- Diabetic kidney disease (nephropathy)
- Diabetic nerve damage (neuropathy)
- Heart disease and stroke
However, A1c targets are individualized — there is no single number that is right for every patient. Your doctor will set a target based on:
- How long you have had diabetes
- Your age and life expectancy
- The presence of other conditions, such as heart disease, kidney disease, or significant complications
- Risk of low blood sugar (hypoglycemia) from diabetes medications
- Other personal factors, including how easily you experience symptoms of low blood sugar
Common alternative targets include:
- Below 6.5% — sometimes recommended for younger patients with newly diagnosed diabetes and few complications, when the target can be reached safely without low blood sugar.
- Below 8.0% or below 8.5% — sometimes appropriate for older adults, those with multiple medical conditions, those at high risk for hypoglycemia, or those with limited life expectancy.
A higher target is not “settling” — for some patients, aiming for an A1c that’s too low can cause more harm than benefit, particularly through episodes of severe low blood sugar.
Estimated average glucose
To make A1c results easier to relate to daily blood glucose monitoring, many laboratories report an estimated average glucose (eAG) alongside the percentage. Approximate conversions:
- A1c 5.0% ≈ 97 mg/dL (5.4 mmol/L)
- A1c 6.0% ≈ 126 mg/dL (7.0 mmol/L)
- A1c 7.0% ≈ 154 mg/dL (8.6 mmol/L)
- A1c 8.0% ≈ 183 mg/dL (10.2 mmol/L)
- A1c 9.0% ≈ 212 mg/dL (11.8 mmol/L)
- A1c 10.0% ≈ 240 mg/dL (13.4 mmol/L)
What can affect A1c accuracy?
The A1c is generally a reliable test, but several conditions can produce results that don’t accurately reflect average glucose levels. Your doctor will consider these when interpreting your result.
Conditions that can falsely lower A1c
- Conditions that shorten red blood cell lifespan. Hemolytic anemia, recent blood loss, and recent blood transfusion can all reduce the average age of circulating red blood cells. Younger red blood cells have had less time to accumulate glycated hemoglobin, so the A1c will be lower than the true average glucose suggests.
- Sickle cell disease and thalassemia. These hereditary hemoglobin disorders can interfere with A1c measurement, sometimes giving falsely low results depending on the specific condition and the laboratory method used.
- Pregnancy. Increased red blood cell turnover during pregnancy can lower A1c values relative to actual glucose levels. For this reason, A1c is generally not used to monitor diabetes during pregnancy; fasting glucose and oral glucose tolerance testing are preferred.
- Erythropoietin therapy and iron supplementation. These can stimulate the production of new (younger) red blood cells, which carry less glycated hemoglobin.
Conditions that can falsely raise A1c
- Conditions that lengthen red blood cell lifespan. Iron deficiency anemia, vitamin B12 deficiency, and folate deficiency can all increase A1c values relative to actual glucose levels because red blood cells are circulating for longer than usual.
- Splenectomy (surgical removal of the spleen) can also lengthen red blood cell lifespan.
- Severe kidney disease and uremia. Can interfere with some A1c assays.
- Some hemoglobin variants. Depending on the laboratory method used, certain genetic hemoglobin variants can artificially raise or lower the A1c result.
If your A1c does not match your daily glucose readings, or if your doctor knows you have a condition that affects A1c accuracy, alternative testing may be used.
Alternative tests when A1c is unreliable
When the A1c may not be accurate, other tests can be used to assess average glucose:
- Fructosamine (also called glycated serum protein, GSP). This test reflects average blood glucose over the past two to three weeks rather than two to three months. It is useful when a shorter-term assessment is needed, when A1c is unreliable, or in pregnancy. Typical reference ranges are approximately 175–280 micromoles per litre (μmol/L) for non-diabetic individuals.
- Continuous glucose monitoring (CGM). A small sensor placed under the skin measures glucose in tissue fluid every few minutes for one to two weeks, generating a detailed profile of glucose levels throughout the day and night. CGM provides a measure called “time in range” — the percentage of time glucose readings stay within target range — that has become an increasingly important alternative to A1c, particularly in patients on insulin.
- Self-monitored blood glucose. Finger-stick glucose readings taken at multiple times during the day can be averaged to estimate overall control when A1c is unreliable.
- Fasting plasma glucose and oral glucose tolerance test can also be used to diagnose and monitor diabetes — see our companion article Understanding your fasting glucose and oral glucose tolerance test.
What happens after an A1c result?
The next steps depend on whether you have known diabetes and what your result shows:
- Normal A1c without diabetes: no immediate action is usually needed. Your doctor may recommend periodic repeat testing depending on your age and risk factors. Adults with risk factors for type 2 diabetes — including overweight, family history, gestational diabetes, polycystic ovary syndrome, or certain ethnic backgrounds — may have A1c repeated every 1–3 years even when results are normal.
- Prediabetes A1c (5.7%–6.4%): lifestyle changes are the main recommendation. Modest weight loss (5–10% of body weight), increased physical activity, and dietary changes can significantly reduce the risk of progressing to diabetes. Some patients benefit from metformin, particularly those at high risk. A repeat A1c in 6–12 months tracks progress.
- Newly elevated A1c suggesting diabetes (≥6.5%): the result is usually confirmed with a repeat test on a separate day or with a fasting glucose test. Once diabetes is confirmed, treatment planning begins. This may include lifestyle changes, oral diabetes medications, injectable medications, or insulin, depending on the situation.
- Above-target A1c in known diabetes: your doctor will discuss possible adjustments to your treatment, including changes to medications, doses, diet, exercise, sleep, stress management, and self-monitoring. Many people require multiple medications to reach target.
- At-target or below-target A1c in known diabetes: usually a sign that current treatment is working. However, particularly low A1c values in patients on insulin or sulfonylurea medications can sometimes indicate frequent unrecognized hypoglycemia, and your doctor may ask about low blood sugar episodes.
- Significantly elevated A1c (above about 9–10%): often prompts more urgent intervention, including consideration of insulin therapy and screening for complications. Patients with newly diagnosed type 2 diabetes and A1c above 10% are sometimes started on insulin from the outset, with the option of stepping down to oral medications later.
Patients with diabetes also typically have other tests done at intervals to screen for complications, including kidney function tests, urine albumin testing, eye examinations, and foot examinations.
Questions to ask your doctor
- What is my A1c, and what does it mean for my health?
- If I have prediabetes, what should I do to reduce my risk of progressing to diabetes?
- If I have diabetes, what is my personal A1c target, and why?
- Am I reaching my target without too much risk of low blood sugar?
- How often should my A1c be checked?
- Are there any conditions I have, such as anemia or a hemoglobin disorder, that could be affecting the accuracy of my A1c?
- If my A1c doesn’t match my home glucose readings, should I use a different test?
- What other tests should I have to screen for diabetes complications?
- Should I be referred to an endocrinologist or diabetes educator?
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