HbA1c is a blood test that shows your average blood sugar over the past two to three months, and it is the main number used to diagnose and monitor diabetes in the UK. If you have just had a result and are not sure what it means, this guide breaks down the ranges in plain English, explains what counts as a good level, and shows how it guides treatment. If you manage diabetes day to day, our diabetes treatments range and our diabetes blog cover the practical side, while your GP or diabetes team interprets your individual results.
Table of Contents
1. What Does HbA1c Actually Measure?
3. What Is a Good HbA1c Level If You Have Diabetes?
6. When HbA1c Can Be Misleading
7.1. What is a normal HbA1c level in the UK?
7.2. Do I need to fast before an HbA1c test?
7.3. Can HbA1c go down?
What Does HbA1c Actually Measure?
HbA1c stands for glycated haemoglobin. Haemoglobin is the protein in red blood cells that carries oxygen. When glucose is in your blood, some of it sticks to haemoglobin, and the more glucose there is, the more sticks. Because red blood cells live for around three months, measuring how much glucose is attached gives a reliable picture of your average blood sugar over that period.
Unlike a finger-prick test, which shows your glucose at a single moment, HbA1c smooths out the daily ups and downs. That is why it is so useful for spotting a longer-term trend rather than a one-off spike.
The UK HbA1c Ranges
In the UK, HbA1c is reported in mmol/mol. The widely used cut-offs are:
- Normal: below 42 mmol/mol (below 6.0%).
- Pre-diabetes (raised risk): 42 to 47 mmol/mol (6.0% to 6.4%).
- Diabetes: 48 mmol/mol (6.5%) or above.
A diagnosis of diabetes is not usually made on a single high reading alone. Unless you have clear symptoms, your GP will normally repeat the test to confirm it. If you are in the pre-diabetes range, it is a signal to act, not a diagnosis of diabetes, and many people bring their level back down with changes to diet, activity and weight.
What Is a Good HbA1c Level If You Have Diabetes?
Targets are individual, but many adults with type 2 diabetes aim for an HbA1c of 48 to 53 mmol/mol. Your own target depends on your age, how long you have had diabetes, which medicines you take, and your overall health. Someone at risk of frequent hypos, for instance, may be given a slightly higher target to keep them safe.
The key point is that lower is not automatically better for everyone. The right number is the one your diabetes team sets with you, balancing good control against the risk of low blood sugar.
How HbA1c Guides Treatment
HbA1c is the yardstick clinicians use to judge whether treatment is working. If your level is above target, your team may suggest changes to lifestyle, adjust your medication, or add a new one. Metformin is often the first medicine prescribed for type 2 diabetes, and you can read more about it on our Metformin product page. Any change is always decided with a prescriber, because the goal is steady, safe control rather than chasing a number.
How Often Is HbA1c Tested?
If your diabetes is stable and well controlled, HbA1c is usually checked roughly twice a year. If your treatment has recently changed or your control is not yet where it should be, it may be tested more often, typically every three months, since that matches the lifespan of the red blood cells the test relies on.
When HbA1c Can Be Misleading
Useful as it is, the HbA1c test is not perfect for everyone. Because it relies on the lifespan of red blood cells, anything that changes that lifespan can skew the result. Conditions such as anaemia, certain blood disorders, recent significant blood loss, and pregnancy can all make HbA1c less reliable, reading either higher or lower than your true average glucose.
In these situations, your clinician may rely more on other tests, such as fasting glucose or direct blood sugar monitoring, to build an accurate picture. This is another reason results should always be interpreted by a professional who knows your full history, rather than judged against the numbers alone.
Important: HbA1c results must be interpreted by a healthcare professional alongside your wider health. This article is general information and does not replace advice from your GP or diabetes team. Prescription diabetes medicines are supplied only after a valid consultation and clinical assessment. You can start a consultation where appropriate.
Frequently Asked Questions
What is a normal HbA1c level in the UK?
Below 42 mmol/mol (under 6.0%) is considered normal. A result of 42 to 47 mmol/mol suggests pre-diabetes, and 48 mmol/mol (6.5%) or above is in the diabetes range, usually confirmed with a repeat test.
Do I need to fast before an HbA1c test?
No. One of the advantages of HbA1c is that it does not require fasting, because it reflects your average glucose over months rather than your level on the day.
Can HbA1c go down?
Yes. Many people lower their HbA1c through changes to diet, physical activity and weight, and through medication where needed. Improvements show up over a few months as newer red blood cells replace older ones.
Is a lower HbA1c always better?
Not for everyone. Very tight control can raise the risk of hypos, especially with certain medicines. Your target should be set individually with your diabetes team.
