HbA1c: your average blood sugar over three months
One number that sums up your blood sugar over the last two to three months, and the thresholds the NHS uses.
What it is
Glucose in your blood sticks to haemoglobin, the protein in red blood cells. Red blood cells live for around three months, so the share of haemoglobin with glucose attached (glycated haemoglobin, or HbA1c) reflects your average blood sugar over the previous two to three months.
That makes it more stable than a single glucose reading, which can change a lot from one hour to the next. You do not need to fast for it.
Why it matters
HbA1c is how the NHS diagnoses type 2 diabetes and spots the stage before it, which the NHS calls non-diabetic hyperglycaemia and is often called prediabetes. Higher levels over years damage small blood vessels in the eyes, kidneys and nerves, and raise the risk of heart disease.
Thresholds in use
UK labs report HbA1c in millimoles per mole (mmol/mol). Older results and many other countries use a percentage.
| Result | mmol/mol | Percent |
|---|---|---|
| Normal | below 42 | below 6.0% |
| Higher than normal (prediabetes) | 42–47 | 6.0–6.4% |
| In the diabetes range | 48 or above | 6.5% or above |
A single result in the diabetes range is usually confirmed with a second test before a diagnosis is made, unless you have symptoms.
HbA1c can read falsely high or low with some conditions that change red blood cells, such as anaemia, some haemoglobin variants, recent blood loss or pregnancy. If your result does not fit the rest of the picture, ask your GP whether another test is more suitable.
In HumanGens: HbA1c sits in the metabolic area with fasting glucose, insulin, weight and waist size, so you can see how they move together.
What moves it
- Weight loss: losing 5–10% of body weight lowers HbA1c for most people who are above a healthy weight.
- Food: fewer refined carbohydrates and sugary drinks, more fibre, and regular meals.
- Activity: both walking and strength training improve how your body handles glucose.
- Sleep: short or poor sleep makes blood sugar harder to control.
- Medication: if you have diabetes, your GP may recommend medicines alongside these changes.
If your result is in the 42–47 range, you may be eligible for the free NHS Diabetes Prevention Programme. Ask your GP practice.
Sources
- National Institute for Health and Care Excellence. Type 2 diabetes: prevention in people at high risk (PH38). 2012, updated 2017.
- National Institute for Health and Care Excellence. Type 2 diabetes in adults: management (NG28). 2015, updated 2022.
- World Health Organization. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus. 2011.
This article is general information, not personal medical advice. Ranges and targets vary by lab and by person; talk to your GP or a qualified clinician about your own results.