Popular Beliefs About HbA1c, and What Is Actually Published
HbA1c: what people commonly get wrong, set against what published UK guidance says.
It needs no fasting and smooths out daily variation, which makes it the standard test for diagnosis and monitoring in the UK.
Key takeaways
- What it reflects: average glucose over 2-3 months
- Diagnostic threshold: 48 mmol/mol (6.5%) or above
- Most useful single change: Ask what your number is and what your target is.
- Commonest mistake: Judging control on a single reading in isolation.
- See a doctor if any of the signs under "When to speak to a doctor" below apply to you.
What the guidance actually says
Before the corrections, the published figures. Everything below is measured against these.
| Measure | Figure |
|---|---|
| What it reflects | average glucose over 2-3 months |
| Diagnostic threshold | 48 mmol/mol (6.5%) or above |
| Non-diabetic hyperglycaemia | 42-47 mmol/mol |
| Common target on diet or one medicine | around 48 mmol/mol |
| Unreliable in | haemoglobinopathies, pregnancy, recent blood loss, advanced kidney disease |
Where people go wrong
Each of these is common, and each is a mistake in the sense that the guidance says otherwise.
- Judging control on a single reading in isolation
- Assuming a good HbA1c means no hypoglycaemia is occurring
- Chasing a very low target if you are frail or at risk of hypos
What to do instead
- Ask what your number is and what your target is
- Understand it is an average; it hides day-to-day swings
- Have it rechecked at the interval your team advises
- Mention sickle cell trait, thalassaemia or recent transfusion, which affect accuracy
The part that is genuinely uncertain
Guidance changes, and it changes because evidence does. The figures above reflect current UK guidance from the bodies named at the foot of this page; where those bodies revise their position, theirs is the account to follow rather than this one.
Where to go next
- Your Questions About HbA1c, Answered
- HbA1c in Five Minutes
- HbA1c — the reference entry
- The Evidence on Diabetic Foot Care, Without the Hype
- The Evidence on Hypoglycaemia, Without the Hype
When to speak to a doctor
Seek urgent help for symptoms of very high glucose with vomiting, abdominal pain, deep breathing or drowsiness. If you take insulin or a sulfonylurea, treat low blood sugar immediately with fast-acting carbohydrate and seek help for repeated episodes or any loss of consciousness.
Where this comes from
How this page was put together
Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.
Medical disclaimer
This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.
Spotted something wrong? Report an error on this page. We correct on the page and say what changed.
