What is HbA1c and what does it measure?
Haemoglobin is the protein in red blood cells that carries oxygen. When glucose (blood sugar) is present, it attaches to haemoglobin — a process called glycation. The more glucose in your blood over time, the more glycated haemoglobin you have.
Because red blood cells live for roughly 2–3 months, HbA1c reflects your average blood glucose concentration over that period. It is not a snapshot of your sugar right now — it is a running average across weeks and months.
HbA1c is reported as a percentage. A result of 6.5%, for example, means that 6.5% of the haemoglobin in your sample was glycated.
HbA1c reference ranges
The table below uses thresholds from major diabetes guidelines. Your lab report will print its own reference interval — use that for your primary comparison.
| HbA1c range | Category | What it generally means |
|---|---|---|
| Below 5.7% | Normal | Blood sugar control within typical range for a non-diabetic adult. |
| 5.7% – 6.4% | Prediabetes | Higher than normal; indicates increased risk of type 2 diabetes without lifestyle changes. |
| 6.5% or above | Diabetes (diagnostic threshold) | Consistent with a diabetes diagnosis when confirmed with a repeat test or another method. |
| Below 7.0% (managed diabetes) | Good control target | A common target for many adults with diagnosed diabetes; individual targets vary. |
Prediabetes: what does it mean in practice?
A prediabetes result (5.7%–6.4%) does not mean you have diabetes. It means your average blood glucose is higher than the typical range and that you have an elevated risk of developing type 2 diabetes, particularly without lifestyle changes.
Research, including the Diabetes Prevention Program trial, has shown that lifestyle changes — particularly increased physical activity and modest weight loss — can significantly reduce the risk of progressing from prediabetes to diabetes. Discuss what the result means for you with your doctor.
Using HbA1c to diagnose diabetes
An HbA1c of 6.5% or above on two separate tests (or confirmed with a fasting glucose or oral glucose tolerance test) meets diagnostic criteria for type 2 diabetes according to guidelines from the American Diabetes Association and the World Health Organization.
A single elevated result is usually confirmed with a repeat test before a diagnosis is made, unless clinical symptoms are present (such as excessive thirst, frequent urination, or unexpected weight loss).
HbA1c as a management tool for diagnosed diabetes
For people already living with diabetes, HbA1c is tested regularly — often every 3–6 months — to assess how well blood sugar is controlled over time. The target varies by individual, but a level below 7.0% is a common goal for many adults with type 2 diabetes without significant hypoglycaemia risk.
Targets may be set higher (e.g., below 8.0%) for older adults, people with frequent low blood sugar episodes, or those with complex health conditions. Stricter targets (below 6.5%) may be appropriate for younger, newly diagnosed patients with good general health.
What can affect HbA1c accuracy?
HbA1c is a reliable test for most people, but several conditions can make it inaccurate — either falsely high or falsely low:
Conditions that may falsely lower HbA1c
- Anaemia (iron, B12, or folate deficiency)
- Haemolytic anaemia (red blood cells are destroyed faster than usual)
- Recent blood transfusion
- Haemoglobin variants (e.g., sickle cell trait) — may interfere with some assay methods
- Chronic kidney disease (can alter red blood cell lifespan)
Conditions that may falsely raise HbA1c
- Iron deficiency anaemia (before treatment)
- Vitamin B12 deficiency
- Splenectomy (removal of the spleen — red blood cells live longer)
- Alcohol excess
If any of these apply, your doctor may order an alternative test — such as fructosamine or a continuous glucose monitor reading — to assess blood sugar control instead.
HbA1c vs fasting glucose: which is better?
Both tests are used for diabetes screening and diagnosis. HbA1c does not require fasting, is more stable between samples, and reflects long-term rather than momentary glucose levels. Fasting glucose, on the other hand, may detect impaired fasting glucose in people who have normal HbA1c.
The two tests do not always agree. Some people will have a normal HbA1c but elevated fasting glucose, or vice versa. This is one reason why clinical context and sometimes multiple tests are used together.
How to read trends, not just single results
One HbA1c reading is useful. A series of readings over time is more useful. If your HbA1c has dropped from 8.2% to 6.9% over six months, that trend is clinically significant — even if 6.9% is technically flagged on the report.
When reviewing your results, keep a note of previous values and bring them to appointments. This helps your care team see whether your blood sugar is moving in the right direction.
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