What this test measures
HbA1c (hemoglobin A1c, sometimes written A1C) measures the percentage of your red blood cells whose haemoglobin has glucose attached to it. Because red blood cells live for about 120 days, the result reflects your average blood sugar over roughly the past 2 to 3 months — not just the moment you give the sample.
Unlike a fasting blood sugar or post-meal blood sugar test, HbA1c is not affected by what you ate that morning or whether you exercised the day before. That makes it the gold-standard for tracking long-term glucose control in people living with diabetes, and one of the diagnostic tests recommended by the American Diabetes Association (ADA) and the World Health Organization (WHO) for detecting type 2 diabetes and prediabetes.
Why it matters
HbA1c is the single most important number in diabetes care. It tells you and your doctor whether your blood sugar has been well-controlled over the last few months — a much more reliable signal than any one-off fingerprick reading. A persistently high HbA1c (above 7% in most adults with diabetes, lower in some cases) is strongly associated with long-term complications: nerve damage (neuropathy), kidney disease (nephropathy), eye disease (retinopathy), heart attack, and stroke. Every 1 percentage point drop in HbA1c reduces the risk of microvascular complications by roughly 35% in landmark trials (UKPDS, DCCT).
For people without a diabetes diagnosis, a single HbA1c can pick up prediabetes (5.7–6.4%) — a stage where lifestyle changes can still prevent or significantly delay the onset of type 2 diabetes. Indian guidelines and the ADA both recommend routine HbA1c screening for adults aged 35 and above, anyone with a BMI ≥23 kg/m² plus a risk factor (family history, hypertension, PCOS, sedentary lifestyle), and pregnant women with risk factors.
How to prepare
No fasting required. HbA1c reflects 2–3 months of average glucose, so a single meal or drink before the test does not affect the result. You can take the test at any time of day.
If you have an ongoing illness (severe infection, recent blood loss, recent transfusion, advanced kidney disease, or known haemoglobinopathy like sickle-cell trait or thalassemia), tell your doctor before testing — these conditions can falsely lower or raise the HbA1c reading and your doctor may order a confirmatory fasting glucose or oral glucose tolerance test instead.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| HbA1c (%)[1][2] | < 5.7% | A very low HbA1c (typically < 4%) is uncommon and may suggest conditions that shorten red blood cell lifespan: haemolytic anemia, recent blood loss, advanced liver disease, or recent blood transfusion. Discuss with your doctor. | 5.7–6.4% indicates prediabetes; ≥6.5% confirms diabetes (when repeated or with classic symptoms + a confirmatory test). The higher the value, the higher the average blood glucose has been over the past 2–3 months. |
| Estimated Average Glucose (eAG) (mg/dL)[1][2] | < 117 mg/dL | A low eAG mirrors a low HbA1c — investigate the same possibilities (haemolysis, blood loss, transfusion). | eAG of 117–137 mg/dL corresponds to prediabetes; ≥140 mg/dL corresponds to diabetes. eAG is computed from HbA1c using the formula 28.7 × HbA1c − 46.7 — it expresses your A1c in the same units as a glucose meter for easier comparison. |
How to read your HbA1c result
| HbA1c (%) | Status | Estimated Average Glucose (mg/dL) | What it usually means |
|---|---|---|---|
| Below 5.7 | Normal | Below 117 | Average glucose in the non-diabetic range |
| 5.7 – 6.4 | Prediabetes | 117 – 137 | Higher than normal; lifestyle changes recommended |
| 6.5 and above | Diabetes | 140 and above | Confirms a diabetes diagnosis (requires a second confirmatory test in asymptomatic patients) |
| Below 7.0 (with diabetes) | Well-controlled | Below 154 | Standard ADA target for most non-pregnant adults with diabetes |
| 7.0 – 8.0 (with diabetes) | Above target | 154 – 183 | Discuss treatment adjustment with your doctor |
| Above 8.0 (with diabetes) | Poorly controlled | Above 183 | Higher risk of long-term complications; treatment intensification usually needed |
Frequently asked questions
Do I need to fast before an HbA1c test?
No. HbA1c reflects your average blood sugar over the past 2–3 months, so a single meal or drink right before the test does not change the result. You can give the sample at any time of day.
How often should I get an HbA1c test?
If you have well-controlled diabetes, twice a year is typical. If your treatment was recently changed or your sugar is not at target, every 3 months is recommended. For screening adults without diabetes, the ADA suggests once every 3 years starting at age 35 (sooner if you have risk factors).
What is a good HbA1c level for someone with diabetes?
The general ADA target for most non-pregnant adults with diabetes is below 7%, which corresponds to an average glucose of about 154 mg/dL. Your individual target may be stricter (6.5%) if you are young and otherwise healthy, or more relaxed (7.5–8%) if you are older, have other major illnesses, or are prone to hypoglycaemia. This should be set with your doctor.
Can HbA1c give a false reading?
Yes, in specific situations. Conditions that shorten red blood cell lifespan (haemolytic anemia, recent blood loss or transfusion, certain medications like erythropoietin) can falsely lower HbA1c. Conditions that lengthen red blood cell lifespan (iron-deficiency anemia, splenectomy) can falsely raise it. Haemoglobinopathies common in India — sickle-cell trait, beta-thalassemia trait — can also interfere depending on the assay method. Tell your doctor if you have any of these so the right test can be chosen.
How is HbA1c different from a fasting blood sugar test?
A fasting blood sugar test measures your blood glucose at one moment in time, after 8 or more hours without food. HbA1c measures your average glucose over 2–3 months. Both are valid for diagnosing diabetes; HbA1c is better for tracking long-term control because it is not affected by what you ate that morning.
Can I lower my HbA1c without medication?
Often yes, especially in prediabetes and early type 2 diabetes. Sustained changes in diet (reducing refined carbs, increasing fibre), regular physical activity (150 minutes a week of moderate exercise), modest weight loss (5–10% of body weight), and better sleep can all lower HbA1c meaningfully. People already on diabetes medication should not stop or change doses without a doctor.
Why does my HbA1c report show eAG too?
eAG (estimated Average Glucose) converts your HbA1c into the same units your home glucose meter uses (mg/dL), so it is easier to compare with your daily readings. The two numbers describe the same underlying control, just in different units.
Is the HbA1c test reliable during pregnancy?
HbA1c can be used in early pregnancy to detect pre-existing diabetes, but it is not the preferred test for gestational diabetes. From 24–28 weeks, an oral glucose tolerance test (OGTT) is the standard. Always follow your obstetrician's guidance.
Related Diabetes / Glucose tests
Tests commonly ordered alongside HbA1c, or that help interpret an unexpected result.
Sources & references
- American Diabetes Association — Standards of Care in Diabetes 2025 · accessed 2026-05-29T00:00:00.000Z
- NIH MedlinePlus — Hemoglobin A1C (HbA1C) Test · accessed 2026-05-29T00:00:00.000Z
- WHO — Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus · accessed 2026-05-29T00:00:00.000Z
- NCBI StatPearls — Glycated Hemoglobin · accessed 2026-05-29T00:00:00.000Z
- UK Prospective Diabetes Study (UKPDS) — long-term complications data · accessed 2026-05-29T00:00:00.000Z
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