Diabetes & metabolic
HbA1c blood test
An HbA1c blood test measures your average blood sugar over the past two to three months, by looking at how much glucose has attached to the haemoglobin in your red blood cells. It is the standard test used to diagnose and monitor type 2 diabetes, and unlike a fasting glucose test it does not need you to fast or depend on a single moment in time.
- What it measures
- Average blood sugar over 2–3 months
- Sample
- Venous blood sample
- Fasting
- Not required
- Also known as
- glycated haemoglobin, haemoglobin A1c, average blood sugar
- Included in 57 Health tests
- 9 panels, from £90
HbA1c reference range
Guide only| Category | Guide range |
|---|---|
| Normal | below 42 mmol/mol |
| Prediabetes (higher risk) | 42–47 mmol/mol |
| Diabetes range | 48 or above mmol/mol |
These are the nationally standardised UK thresholds (WHO/NICE), the same whichever accredited lab runs the test, so HbA1c is less lab-dependent than most markers. In older units, 48 mmol/mol is 6.5% and 42 mmol/mol is 6.0%. A diagnosis of diabetes is normally confirmed with a repeat test, and HbA1c can read falsely low or high with anaemia, some haemoglobin variants, pregnancy or recent blood loss, so it is read alongside your wider picture.
These are general UK adult guide ranges from public health sources, shown for orientation only. Reference ranges vary by laboratory, assay, age and sex, so your result is always interpreted against the range quoted by the analysing laboratory on your report.
What does a high HbA1c level mean?
A high HbA1c means your average blood sugar has been running high. A result of 48 mmol/mol or above is in the diabetes range, and 42 to 47 mmol/mol is the prediabetes range, where blood sugar is higher than ideal and there is a raised risk of going on to develop type 2 diabetes.
A single raised result is usually repeated to confirm it, and it is interpreted with your symptoms and risk factors. A prediabetes result is often reversible: losing excess weight, moving more and changing your diet can bring HbA1c back down, which is one reason testing early is worthwhile.
What does a low HbA1c level mean?
A low HbA1c simply means your average blood sugar has been low, which is usually normal and reassuring. In people on diabetes treatment, a low result can sometimes signal blood sugar dropping too far (hypoglycaemia), so treatment is reviewed.
Occasionally HbA1c reads lower than your true average because red blood cells are being replaced faster than usual, for example with recent blood loss, a haemolytic anaemia or in pregnancy. In those situations a glucose test can give a clearer picture.
When to consider an HbA1c test
- A family history of type 2 diabetes
- Carrying extra weight, especially around the middle
- Raised blood pressure or cholesterol
- Increased thirst, tiredness or passing urine more often
- Polycystic ovary syndrome (PCOS)
- South Asian, African or African-Caribbean heritage (higher risk)
- Keeping an eye on prediabetes or a prevention plan
Frequently asked questions
This page is general information about a blood marker and is not medical advice or a diagnosis. An HbA1c test screens and gives context; results are interpreted by a clinician alongside your symptoms, history and other markers. Always follow the guidance on your own report.