HbA1c: Common Questions
A blood test reflecting average blood glucose over the preceding two to three months.
Last revised
HbA1c: the questions people actually ask, answered from published guidance.
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 get help" below apply to you.
What is HbA1c?
A blood test reflecting average blood glucose over the preceding two to three months.
Why does it matter?
It needs no fasting and smooths out daily variation, which makes it the standard test for diagnosis and monitoring in the UK.
What it reflects for HbA1c?
Average glucose over 2-3 months.
Diagnostic threshold for HbA1c?
48 mmol/mol (6.5%) or above.
Non-diabetic hyperglycaemia for HbA1c?
42-47 mmol/mol.
Common target on diet or one medicine for HbA1c?
Around 48 mmol/mol.
What is the single most useful thing to do?
Ask what your number is and what your target is.
What is the most common mistake?
Judging control on a single reading in isolation.
When should I see 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 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 get help
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.
