HbA1c Normal Range and Levels: How to Understand Your Result
What HbA1c actually measures, what counts as a normal, prediabetes or diabetes-range result, and why it should be read alongside your symptoms and other results.
If you’ve had an HbA1c test, the number that comes back rarely explains itself.
Is 42 fine? Is 48 something to worry about? And why is your result in mmol/mol when every chart online seems to be in percentages?
And more importantly, what does it mean for your health?
This guide walks through what HbA1c actually measures, what counts as a normal, prediabetes or diabetes-range result.
You’ll also understand how HbA1c is a useful average, and why it’s read alongside your symptoms and other results.
What is HbA1c, and what does it measure?
HbA1c stands for glycated haemoglobin. It is a blood test that shows your average blood glucose level over the past 2–3 months.
Glucose naturally attaches to haemoglobin, the protein in red blood cells that carries oxygen around your body. When there is more glucose in your blood, more of it attaches to haemoglobin.
Because red blood cells typically live for around three months, measuring glycated haemoglobin gives an overall picture of your blood glucose during this period, with slightly more influence from the most recent few weeks.
And here’s what you need to remember about HbA1c:
- It shows an average, not a single reading. A finger-prick or fasting glucose test shows your blood glucose at one particular moment. HbA1c gives a broader picture by reflecting your average levels over time.
- The results may not always match other glucose tests. You can have a normal HbA1c and a high glucose reading, or the other way around, because each test measures something slightly different.
- You usually do not need to fast for HbA1c. However, if it is included as part of a wider blood test panel, you may be asked to fast for other tests, such as fasting glucose or fasting insulin. Check the instructions for your appointment.
- It is one part of a wider assessment. A clinician may consider your HbA1c alongside glucose, insulin, cholesterol, liver function, weight, waist circumference, family history and other risk factors when assessing your risk of diabetes.
What is a normal HbA1c range?
Here’s a quick view of the range used for your HbA1c test. They’re a helpful frame of reference, but reference ranges can vary slightly by laboratory, and HbA1c is not meant to be read in isolation.
| Category | HbA1c (%) | HbA1c (mmol/mol) |
|---|---|---|
| Normal (below prediabetes threshold) | Below 5.7% | Below 39 |
| Prediabetes / increased risk | 5.7–6.4% | 39–46 |
| Diabetes range | 6.5% or above | 48 or above |
A result in the diabetes range on a single test does not automatically confirm diabetes for everyone. Diagnosis usually needs confirmation, for example a repeat HbA1c, a fasting glucose or an oral glucose tolerance test, and takes your symptoms into account.
Equally, a result below these thresholds does not always rule diabetes out, particularly if you have symptoms of high blood sugar or a condition that affects your red blood cells (more on that below).
HbA1c in percentage vs mmol/mol
In the UK, HbA1c is now reported in mmol/mol under the IFCC standard. You’ll still see the older percentage figures (the NGSP/DCCT format) on many charts and in a lot of research, which is where the confusion tends to start.
The table below is an approximate conversion to help you translate between the two. Treat it as a guide, not a precise calculator.
| HbA1c (%) | HbA1c (mmol/mol, approx.) |
|---|---|
| 5.7% | 39 |
| 6.0% | 42 |
| 6.5% | 48 |
| 7.0% | 53 |
| 8.0% | 64 |
| 9.0% | 75 |
| 10.0% | 86 |
Is 42 or 48 mmol/mol high? Using the bands above, around 42 mmol/mol sits in the prediabetes range, and 48 mmol/mol is at the diabetes threshold. But a number on its own doesn’t tell you what to do next — that depends on whether it’s a first result, whether you have symptoms, and what your clinician recommends.
When HbA1c can be misleading
HbA1c is a useful test, but it does not give a reliable picture of average blood glucose in every situation. This is because the result depends partly on how long your red blood cells live and how much haemoglobin they contain.
If something changes your red blood cells, your HbA1c result may appear higher or lower than your actual average blood glucose. This can happen with:
- Some haemoglobin variants, including inherited conditions such as sickle cell disease or thalassaemia.
- Recent blood loss, haemolysis or a blood transfusion, because these can change the age and number of red blood cells in your circulation.
- Iron-deficiency anaemia, which can sometimes make HbA1c appear higher than expected.
- Chronic kidney disease, particularly more advanced disease.
- Pregnancy, when healthcare professionals may use other tests to assess blood glucose, depending on the stage of pregnancy and the reason for testing.
This does not mean HbA1c is unsuitable for everyone with these conditions. It means the result may need to be interpreted more carefully, and another type of glucose test may sometimes be more appropriate.
If your HbA1c result seems unexpected or does not match your other test results, do not try to diagnose yourself from a chart. Speak to a clinician, who can consider your medical history and decide whether you need further testing. HbA1c should be interpreted as part of the wider picture of your health, rather than on its own.
What to do if your HbA1c is unexpected
An HbA1c result that is higher or lower than expected does not tell the whole story. Speak to your GP or a clinician before making changes to your diet or medication based on one result.
They may recommend repeating the test or using another test, such as fasting glucose or an oral glucose tolerance test. Your symptoms, weight, family history, medication and any conditions affecting your red blood cells will also help put the result into context.
How much does an HbA1c blood test cost in London?
A standalone private HbA1c test in London typically costs around £39–£95, depending on the clinic, the type of sample taken and how quickly you receive your results. For example, some clinics advertise HbA1c testing from £39–£49, while others charge around £63–£95.
However, the advertised test price may not be the final amount you pay. Some providers charge separately for the blood draw, GP appointment, result interpretation or written report. For example, one London clinic lists a £63 HbA1c test alongside a £50 phlebotomy fee, while another lists additional GP and handling fees separately.
A single HbA1c result can also be difficult to interpret on its own. If the result is borderline, unexpected or suggests an increased risk of diabetes, you may need additional tests such as fasting glucose, fasting insulin, cholesterol and liver function tests, as well as a clinical review.
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Rather than paying separately for an HbA1c test, additional markers and an appointment to discuss the results, you receive a complete assessment. This gives you a clearer understanding of your overall metabolic health and practical next steps to help reduce your future risk of type 2 diabetes.
You can book directly, without waiting on a referral, and discuss what your result means and what (if anything) to do next.
Frequently Asked Questions
What is a normal HbA1c in the UK?
A normal HbA1c is generally below 42 mmol/mol (below 6.0%), with below 39 mmol/mol (5.7%) considered below the prediabetes threshold. Results of 39–46 mmol/mol suggest increased risk (prediabetes), and 48 mmol/mol or above falls in the diabetes range. Laboratory ranges can vary slightly, and results are interpreted alongside your symptoms and other tests.
Is 42, 48 or 58 mmol/mol high for a HbA1c test?
Roughly speaking, 42 mmol/mol sits in the prediabetes range, 48 mmol/mol is at the diabetes threshold, and 58 mmol/mol is within the diabetes range. What matters next depends on whether it’s a first result, whether you have symptoms and what your clinician advises — a single value doesn’t decide the diagnosis by itself.
What’s the difference between HbA1c percentage and mmol/mol?
They measure the same thing using different scales. The UK now reports HbA1c in mmol/mol (the IFCC standard), while the older percentage figures (NGSP/DCCT) still appear in many charts and studies. For example, 6.5% is approximately 48 mmol/mol.
Can anaemia affect HbA1c?
Yes. Iron-deficiency anaemia and other conditions that change red blood cell turnover can make HbA1c read higher or lower than your true average glucose. This is one reason an unexpected result should be discussed with a clinician rather than taken at face value.
Does HbA1c diagnose diabetes on its own?
Not usually. A single result in the diabetes range typically needs confirmation — for example a repeat HbA1c or a glucose test — and is interpreted alongside your symptoms. In some situations, such as pregnancy or certain blood conditions, HbA1c isn’t the preferred test at all.
How often should HbA1c be checked?
It depends on your situation. People with diabetes are often tested every few months to every six months, while those at risk may be checked less frequently. Your clinician will recommend a schedule based on your results, treatment and overall health.
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