You have had a blood test, and somewhere on the report is a line that says HbA1c with a number next to it: 38, perhaps, or 44, or 51. Maybe a GP mentioned “pre-diabetes” in passing, or a relative has just been diagnosed with type 2 diabetes and you want to know where you stand. Either way, the number matters, and it is one of the few blood results where a small shift can genuinely change what you do next.
This guide explains what HbA1c actually measures, what the NICE ranges mean in plain English, why the band from 42 to 47 is the one worth paying attention to, and when the test can mislead. At WMG Health, our private blood testing clinic at 134 Harley Street, London, every result is reviewed by a GMC-registered doctor and no GP referral is needed.
What HbA1c actually measures
Glucose (sugar) in your bloodstream sticks to haemoglobin, the oxygen-carrying protein inside your red blood cells. The more glucose there is in your blood over time, the more haemoglobin ends up “glycated”, which is what the “glycated haemoglobin” in the full name refers to.
Red blood cells live for about 120 days, so the HbA1c test gives a picture of your average blood sugar over the previous two to three months (NICE’s clinical summary puts it at 8 to 12 weeks). That is what makes it so useful. A single glucose reading tells you about one moment, and it moves with what you ate that morning. HbA1c smooths much of that out.
Two practical consequences follow:
- You do not need to fast. Not needing to fast is one of the recognised advantages of HbA1c over a glucose test, so breakfast before the test is fine.
- One indulgent week will not define your number. Because HbA1c is an average over several weeks, a short burst of festive eating has a limited effect on it. Our after-Christmas blood test guide covers what is and is not worth checking in January.
What the numbers mean
UK laboratories report HbA1c in mmol/mol. You may also see the older percentage units, particularly on overseas reports or in older NHS letters. The ranges below are the ones used in NICE guidance on preventing type 2 diabetes (PH38) and in the NICE Clinical Knowledge Summary on type 2 diabetes.
| HbA1c (mmol/mol) | Old units (%) | What it means |
|---|---|---|
| Below 42 | Below 6.0% | Normal range |
| 42 to 47 | 6.0 to 6.4% | Higher risk of type 2 diabetes (often called pre-diabetes; clinically, non-diabetic hyperglycaemia) |
| 48 or above | 6.5% or above | In the diabetes range |
A few points that the table alone does not tell you:
- If you have no symptoms, a single result of 48 or above is not enough for a diagnosis. A repeat test, preferably the same type of test, is needed to confirm it. If you do have symptoms of diabetes (see below), a doctor can use a single result, although repeat testing is still sensible.
- A result under 42 is not the end of the story if you have other risk factors. NICE suggests that people with a high risk score but an HbA1c below 42 are reassessed at least every three years.
- If you already have diabetes, your target is agreed individually with your diabetes team and depends on your treatment. The ranges above are for diagnosis and screening, not for managing existing diabetes.
Why 42 to 47 is the number worth acting on
This is the band most people are surprised by, and it is also the most useful place to find yourself, because it is the stage where there is still time to change direction.
A result of 42 to 47 mmol/mol means your blood sugar is running higher than it should, but you do not have diabetes. NICE guidance (PH38) describes this as being at high risk of type 2 diabetes. It recommends support to change diet, physical activity and weight, including referral to an intensive lifestyle-change programme, and a repeat blood test at least once a year. In England, people at risk may be eligible for the Healthier You NHS Diabetes Prevention Programme, which your GP practice can refer you to.
The reassuring part is that type 2 diabetes is not inevitable from here. The NHS says the risk can be reduced through lifestyle changes, and that it may be possible to prevent type 2 diabetes by losing weight and improving your diet. NHS England reports that completing the Healthier You programme cuts the risk of developing type 2 diabetes by more than a third. The earlier you know your number, the more room you have to change its direction.
Symptoms of high blood sugar
Many people with raised blood sugar have no obvious symptoms; as the NHS puts it, not everyone with type 2 diabetes has symptoms. That is exactly why a test is useful. When symptoms do appear, the NHS lists:
- feeling very tired
- peeing more than usual
- feeling thirsty all the time
- losing weight without trying to
- blurred vision
- cuts or wounds taking longer to heal
- itching around the penis or vagina, or getting thrush repeatedly
Tiredness in particular is easy to put down to work, winter or age. If you are tired all the time, blood sugar is one of the causes worth ruling out, alongside iron, thyroid and vitamin D. Our guide to always feeling tired covers the full list.
See a GP if you think you may have type 2 diabetes, or if you know you are at higher risk. Call 999 or go to A&E if you think you have high blood sugar and you are feeling or being sick or have tummy pain, are breathing more quickly than usual or your heart is beating faster than usual, feel drowsy or are struggling to stay awake, feel confused or find it hard to concentrate, or your breath smells fruity (like pear drop sweets). Do not drive yourself: ask someone to take you or call an ambulance. These can be signs of a serious complication of high blood sugar and need urgent medical assessment, not a routine blood test.
Who should think about checking their HbA1c
The NHS says you may be more likely to get type 2 diabetes if:
- you are white and over 40, or over 25 and from a South Asian, Chinese, Black African or Black Caribbean background
- a parent, brother or sister has type 2 diabetes
- you are overweight and not very physically active (unexplained weight gain is worth investigating in its own right)
- you have a condition that increases your risk, such as high blood pressure
NICE guidance (PH38) adds other conditions that raise the risk, including a history of diabetes in pregnancy (gestational diabetes), cardiovascular disease, stroke, mental health problems and, in women, PMOS (formerly known as PCOS), which is linked with insulin resistance; see our PCOS / PMOS symptoms page.
If any of these apply to you, and particularly if two or more do, it is worth knowing your HbA1c. It pairs naturally with a cholesterol check, since diabetes and raised cholesterol both add to your risk of heart disease and stroke.
When HbA1c can be misleading
Because HbA1c depends on red blood cells, anything that changes how long those cells live, or the type of haemoglobin inside them, can push the result up or down without your blood sugar actually changing. The NICE Clinical Knowledge Summary advises caution with HbA1c in people with:
- severe anaemia of any cause, including iron deficiency anaemia
- haemoglobin variants, such as sickle cell trait. In Black people, including those who may have undiagnosed sickle cell trait, HbA1c can underestimate blood sugar
- a shortened or altered red cell lifespan, for example after removal of the spleen
- a recent blood transfusion
It also says HbA1c should not be used to diagnose diabetes in some groups, including:
- pregnancy, or within two months of giving birth
- symptoms of diabetes that started less than two months ago
- end-stage kidney disease
- people who are acutely ill, or taking medicines that can raise blood sugar, such as long-term steroids
- children and young people under 18
In these situations a clinician may prefer a fasting glucose test or an oral glucose tolerance test. This is one reason it is worth checking HbA1c alongside a full blood count and ferritin: if you turn out to be anaemic or low in iron, the doctor reviewing your results can take that into account before reading anything into your HbA1c.
HbA1c, fasting glucose and fasting insulin: which one?
- HbA1c is one of the standard UK tests for diabetes and for identifying people at high risk. No fasting, and it reflects the last two to three months.
- Fasting glucose is a snapshot of your blood sugar after an overnight fast. NICE PH38 uses 5.5 to 6.9 mmol/L as the high-risk band, and 7.0 mmol/L or above is in the diabetes range (again needing confirmation if you have no symptoms). It is useful when HbA1c may be unreliable.
- Fasting insulin shows how hard your pancreas is working to keep glucose normal. It is not part of NHS diabetes diagnosis, but some clinicians use it alongside glucose when insulin resistance is suspected, for example in PMOS. It needs a strict overnight fast.
For most people with no reason to doubt the result, HbA1c on its own is a sensible first test.
Getting tested at WMG Health
HbA1c is included in our General Wellness panel (£279), alongside a full blood count, iron studies including ferritin, vitamin D, B12 and folate, thyroid function, liver and kidney function, a lipid profile (cholesterol), CRP and ESR, and zinc. That gives you blood sugar plus the blood count and iron picture that helps the doctor interpret it, and the cholesterol result that sits alongside it in your cardiovascular risk.
If you only want HbA1c, or want it alongside one of our other panels, you can build a custom panel, where a clinician confirms the price in writing before you book. Fasting glucose and fasting insulin are not part of any fixed panel, but can be added to a custom panel if a clinician thinks they are useful for you. Our New Year health check guide explains how to choose a sensible panel without paying for markers you do not need.
Results are released as each marker is reviewed by a GMC-registered doctor, and we confirm the expected timeframe when you book. If your HbA1c is in the higher-risk or diabetes range, we will explain what it means and recommend that you share it with your GP, who can arrange any confirmatory testing and ongoing NHS care.
Common questions
Do I need to fast for an HbA1c test? No. HbA1c reflects the previous two to three months, so you do not need to fast for it. If fasting glucose or fasting insulin are added to the same draw, those do need an overnight fast. Our General Wellness panel, which includes HbA1c, does need a fast of at least 12 hours, with water only, because of the other markers on the panel, such as iron studies and triglycerides.
My HbA1c is 43. Do I have diabetes? No. A result of 42 to 47 mmol/mol means you are at higher risk of developing type 2 diabetes, not that you have it. It is a good time to make changes, and NICE recommends a repeat blood test at least once a year.
How quickly can I bring my HbA1c down? Because it reflects roughly the last two to three months, retesting much sooner than about three months after a change will not show the full effect. The NHS says the risk of type 2 diabetes can be reduced through lifestyle changes such as losing weight and improving your diet.
Can Christmas or a holiday push my HbA1c up? A short period of heavier eating has a limited effect on a two-to-three-month average. A sustained change over the winter can show, which is why the trend across several tests tells you more than one result.
Does alcohol affect blood sugar? Alcohol is high in calories, so regular heavy drinking can contribute to weight gain, which is one of the main risk factors for type 2 diabetes. Our guide to Dry January and your liver covers what liver blood tests can show.
Do I need a GP referral? No. WMG Health is direct-access. If a result needs follow-up, we will tell you and suggest that you share it with your GP.
Sources
- NICE Public Health Guideline PH38: Type 2 diabetes: prevention in people at high risk. nice.org.uk
- NICE Clinical Knowledge Summary: Diabetes, type 2 (diagnosis in adults). cks.nice.org.uk
- NICE Guideline NG28: Type 2 diabetes in adults: management. nice.org.uk
- NHS: Type 2 diabetes (symptoms and who is more likely to get it). nhs.uk
- NHS: Diabetes (pre-diabetes). nhs.uk
- NHS: High blood sugar (hyperglycaemia). nhs.uk
- NHS England: Healthier You NHS Diabetes Prevention Programme. england.nhs.uk
This article is for general information only and does not constitute clinical advice. If you have concerns about your blood sugar or symptoms, book an appointment or speak to your GP.