Key takeaways
- HbA1c gives an average picture of your blood sugar over the past 2 to 3 months, reported in mmol/mol, rather than a single snapshot.
- Blood London's HbA1c test costs £71.25 plus the £50 blood draw, with results back in 1 day, and no fasting is needed.
- NICE and NHS thresholds are well established: below 42 mmol/mol is normal, 42 to 47 is prediabetes or non-diabetic hyperglycaemia, and 48 or above is in the diabetes range.
- If you have no symptoms, a result of 48 mmol/mol or above is confirmed with a repeat test before diabetes is diagnosed.
- Conditions such as anaemia, certain haemoglobin variants and pregnancy can affect the accuracy of an HbA1c result, so your doctor considers these alongside the number.
- Because HbA1c reflects an average, you don't need to fast before the test, unlike some other blood sugar checks.
HbA1c measures the proportion of sugar attached to your red blood cells, giving an average picture of your blood sugar over the past 2 to 3 months rather than a single reading. NICE and NHS guidance use established thresholds: below 42 mmol/mol is normal, 42 to 47 is prediabetes, and 48 or above is in the diabetes range. You can book an HbA1c blood test at Blood London without a GP referral.
Book an HbA1c blood test at 117a Harley Street: £71.25 plus the £50 blood draw, results back in 1 day.
What does HbA1c actually measure?
HbA1c measures the percentage of haemoglobin, the protein in red blood cells that carries oxygen, that has sugar attached to it. Because red blood cells last around 2 to 3 months, the result reflects your average blood sugar over that whole period rather than what you ate that morning. This is why HbA1c is used differently from a fasting glucose test, which only shows your blood sugar at the moment of the sample.
What do the different HbA1c results mean?
NICE and NHS guidance set out three established bands. Below 42 mmol/mol is considered normal. A result of 42 to 47 mmol/mol falls into prediabetes, sometimes called non-diabetic hyperglycaemia, meaning your blood sugar is higher than normal but not yet in the diabetes range. A result of 48 mmol/mol or above is in the diabetes range. If you have no symptoms, the result is confirmed with a second test before diabetes is diagnosed; if you have typical symptoms, a doctor may diagnose it from one result.
| HbA1c result | What it generally means |
|---|---|
| Below 42 mmol/mol | Normal |
| 42 to 47 mmol/mol | Prediabetes (non-diabetic hyperglycaemia) |
| 48 mmol/mol or above | Diabetes range (confirmed by a repeat test if you have no symptoms) |
NICE and NHS established thresholds. Your doctor reads the result alongside your symptoms and history.
Do I need to fast before an HbA1c test?
No. Because HbA1c reflects an average over months rather than your blood sugar at that moment, no fasting is needed, and you can eat and drink normally beforehand. This is different from a fasting glucose test, which does need preparation, so if your doctor has ordered both together, ask which parts require fasting.
Can other health conditions affect my HbA1c result?
Yes. Anaemia and certain haemoglobin variants can affect how accurate an HbA1c result is, because the test relies on the normal lifespan and structure of red blood cells. Recent blood loss or a blood transfusion, kidney disease and some medicines can also affect it. Pregnancy changes the result too, and diabetes in pregnancy is usually assessed with a glucose tolerance test instead. If you have any of these, your doctor takes it into account rather than reading the HbA1c figure alone.
What happens if my HbA1c is raised?
If you have no symptoms, a single raised result doesn't confirm diabetes on its own: a repeat test is used to confirm it, and your doctor will also consider your symptoms, weight, family history and other risk factors. If your result sits in the prediabetes range, that's usually a prompt for lifestyle changes and closer monitoring, discussed with your doctor rather than acted on from the number in isolation. If you are very thirsty, passing a lot of urine, losing weight without trying, or feel very unwell, drowsy or are vomiting, get medical advice the same day through your GP or NHS 111, or call 999 if you are seriously unwell.
Are there tests that look at diabetes risk in more detail than HbA1c alone?
Yes. Diabetic Profile 1 pairs HbA1c with a fasting glucose reading, giving both a snapshot and a trend from one visit (£83.75 plus the £50 blood draw, results in 1 day; the glucose part needs an 8-hour fast). The insulin resistance blood test adds a fasting insulin resistance index alongside HbA1c and a lipid profile (£279 plus the £50 blood draw, results in 1 working day, 10 to 12 hour fast). For the broadest single-visit panel, the complete metabolic blood test adds thyroid, liver, kidney and uric acid markers (£675 plus the £50 blood draw, results in up to 9 working days, 10 to 12 hour fast). If you would like a doctor to go through your result, you can add a doctor review to your test for £75. What type 2 diabetes means for you specifically is a conversation for your GP rather than the blood result alone.
How HbA1c testing works at our Harley Street clinic
The HbA1c blood test is one of our most popular private blood tests in London, costing £71.25 plus the £50 blood draw, with no fasting needed. Results are sent by email, usually within 1 day. You can walk in or book online at 117a Harley Street, seven days a week, with no GP referral needed. If you'd like these markers alongside a doctor's examination and a wider health assessment, the Full Body MOT health check includes HbA1c as part of a broader review.
Book your HbA1c blood test online or walk in at 117a Harley Street: £71.25 plus the £50 blood draw, results by email in 1 day. Start your booking.
Frequently asked questions
Is HbA1c the same as a blood sugar test?
Not quite. A standard glucose test shows your blood sugar at the moment of the sample, while HbA1c gives an average over the past 2 to 3 months, so the two tests answer slightly different questions.
Can I have a normal HbA1c and still have diabetes?
It's uncommon but possible, for example where a condition affecting red blood cells makes the result less reliable, or where blood sugar has risen quickly. This is one reason your doctor considers your symptoms and other risk factors alongside the HbA1c figure.
How quickly does HbA1c change?
Because it reflects an average over 2 to 3 months, HbA1c changes more slowly than day-to-day blood sugar. It's not a test for checking short-term changes, such as what you ate that day.
Does HbA1c diagnose type 1 diabetes?
HbA1c is mainly used for type 2 diabetes and prediabetes assessment. Type 1 diabetes can develop quickly, so HbA1c may not yet be raised; if you have symptoms such as thirst, passing a lot of urine and weight loss, see a doctor the same day.
Do I need to repeat my HbA1c test if it comes back raised?
Usually, yes. If you have no symptoms, a result in the diabetes range is confirmed with a repeat test before diabetes is diagnosed.
Will losing weight lower my HbA1c?
For many people, weight loss, diet changes and increased activity can improve HbA1c over time, particularly in prediabetes. Whether that's enough on its own, or whether treatment is also needed, is a decision for your doctor based on your full picture.
References
- Type 2 diabetes in adults: management (NICE)
- Type 2 diabetes (NHS)
- Diabetes, type 2 (NICE CKS)
- HbA1c (Diabetes UK)