HbA1c — pronounced "haemoglobin A1c" — is a blood test that measures your average blood sugar (glucose) level over the past 2 to 3 months. Unlike a fasting glucose test, which gives you a single snapshot, HbA1c reflects a longer-term picture of how well your blood sugar is controlled. It is the gold standard test for diagnosing type 2 diabetes and monitoring diabetes management in the UK.
Note: This article is for educational purposes. If your HbA1c is outside the normal range, please speak to your GP or diabetes nurse as soon as possible.
What Is HbA1c, Exactly?
Haemoglobin is the protein in red blood cells that carries oxygen. When glucose (sugar) is present in the blood, it sticks to haemoglobin in a process called glycation. The HbA1c test measures the percentage of haemoglobin that has glucose attached to it.
Because red blood cells live for approximately 8–12 weeks before being replaced, HbA1c gives an average picture of your blood glucose over that period. This makes it far more useful than a one-off glucose reading, which can be temporarily affected by a recent meal, stress, or illness.
HbA1c Units: mmol/mol vs %
In the UK, HbA1c results are reported in millimoles per mole (mmol/mol), which replaced the older percentage (%) system. You may see both on older results. Here is how they compare:
| Category | mmol/mol (UK) | % (old system) |
|---|---|---|
| Normal (non-diabetic) | Below 42 mmol/mol | Below 6.0% |
| Pre-diabetes | 42–47 mmol/mol | 6.0–6.4% |
| Diabetes (diagnostic threshold) | 48 mmol/mol or above | 6.5% or above |
| Well-controlled diabetes (target) | 48–53 mmol/mol | 6.5–7.0% |
| Poorly controlled / high risk | Above 75 mmol/mol | Above 9.0% |
What Does a Normal HbA1c Mean?
A result below 42 mmol/mol (6.0%) is considered normal and indicates that your blood sugar is well regulated. If you are at risk of diabetes (due to obesity, family history, or previous high results), your GP may recommend annual monitoring to detect any changes early.
What Is Pre-diabetes?
A result between 42 and 47 mmol/mol (6.0–6.4%) indicates pre-diabetes — also called non-diabetic hyperglycaemia. This means your blood sugar is higher than normal but not yet in the diabetic range.
Pre-diabetes is a warning sign. Without intervention, many people with pre-diabetes will go on to develop type 2 diabetes within 5–10 years. However, the good news is that pre-diabetes is often reversible. Evidence shows that lifestyle changes — particularly losing weight (if overweight), increasing physical activity, and improving diet — can return blood sugar to normal and significantly reduce the risk of developing diabetes.
If your HbA1c is in the pre-diabetic range, your GP may refer you to the NHS Diabetes Prevention Programme, a free, evidence-based programme that helps you make sustainable lifestyle changes.
What Does an HbA1c in the Diabetic Range Mean?
An HbA1c of 48 mmol/mol (6.5%) or above on two separate tests is used to diagnose type 2 diabetes in the UK (a single high result may be used in the presence of clear symptoms). Type 1 diabetes is usually diagnosed in different ways, as it typically presents with acute symptoms requiring urgent medical assessment.
For people already diagnosed with diabetes, the HbA1c is used to monitor how well blood sugar is being controlled. The NHS target for most people with type 2 diabetes is 48–53 mmol/mol, though your individual target may differ based on your circumstances.
Factors That Can Affect HbA1c Results
HbA1c is generally a reliable test, but certain conditions can affect the result:
- Anaemia: Iron deficiency anaemia or haemolytic anaemia can falsely lower HbA1c because red blood cell lifespan is shortened.
- Haemoglobin variants: Certain inherited haemoglobin conditions (such as sickle cell trait or thalassaemia) can affect the accuracy of HbA1c.
- Kidney disease: Chronic kidney disease can alter red blood cell turnover and affect HbA1c.
- Recent blood loss or transfusion: These alter the proportion of older glycated cells, affecting the result.
- Pregnancy: HbA1c is not used to diagnose gestational diabetes; a glucose tolerance test is used instead.
If any of these factors apply to you, your GP may use a different test such as a fasting glucose or glucose tolerance test to assess your blood sugar more accurately.
How Can I Lower My HbA1c?
If your HbA1c is in the pre-diabetic or diabetic range, the following evidence-based interventions are most effective:
- Weight loss: Even a 5–10% reduction in body weight can significantly improve blood sugar control.
- Physical activity: Aim for at least 150 minutes of moderate-intensity aerobic activity per week, plus strength training twice weekly.
- Dietary changes: Reducing refined carbohydrates and sugar, increasing fibre, vegetables, lean protein, and healthy fats, and following a low-GI eating pattern.
- Medication: For type 2 diabetes, your GP may prescribe metformin or other glucose-lowering medications if lifestyle changes alone are insufficient.
- Blood glucose monitoring: Self-monitoring can help you understand how specific foods and activities affect your blood sugar.
⚠️ If your HbA1c result suggests diabetes or pre-diabetes, please make an appointment with your GP as soon as possible. Early intervention significantly improves long-term health outcomes.
How Often Should HbA1c Be Tested?
- No diabetes, no risk factors: Not routinely tested unless symptoms are present.
- Pre-diabetes: Usually retested every 6–12 months.
- Well-controlled type 2 diabetes: Typically every 6 months.
- Poorly controlled or recently changed treatment: Every 3 months until stable.
🔬 Get Your Results Explained Instantly
Upload your blood test or imaging report and receive a clear, plain-English AI interpretation in under 60 seconds.
Analyse My Results →