Explainer · updated 2026-09-09
HbA1c, explained in plain English
Key facts
- Typical adult reference interval: 4-5.6 % (ABIM)
- Level at or above which the result meets the diagnostic definition of diabetes: 6.5 % (ADA 2026)
- Prediabetes band: 5.7-6.4 % (ADA 2026)
- What HbA1c measures: the share of haemoglobin that sugar has stuck to, reflecting average glucose over the last two to three months (ADA 2026)
What it is
HbA1c is the share of your haemoglobin that sugar has stuck to. It builds up slowly, so the number reflects your average glucose over the last two to three months. That smooths out the day-to-day swings that a single glucose reading picks up.
What the number is telling you
Because HbA1c moves slowly, it shows direction. Two or three results a few months apart tell you where your glucose control is heading, where a single glucose reading only tells you about that moment. One reading on its own says little.
What high or low can mean
High: A result at or above 6.5 per cent meets the diagnostic definition of diabetes, and 5.7 to 6.4 per cent is the prediabetes band beneath it. Those are the lines the definition uses; where your result sits, and what it means for you, is for your doctor to say.
Low: A low result is less common, and it is often a question of the red cells themselves. Anything that shortens their life makes HbA1c read low and can hide real glucose levels behind a normal-looking number.
What a typical result looks like
Typical adult reference intervals from ABIM run from 4 to 5.6 per cent. The range on your own report is the one that counts.
Questions worth asking your doctor
- What does my result mean for me, and where does it sit?
- How often should this test be repeated?
- If my level is high, what changes are worth trying, and how will we track them?
- Could anything about my red cells make this number read lower than my real glucose level?
If a result worries you, ask your doctor.
Sources
- ABIM Laboratory Test Reference Ranges (2026)
- Standards of Care in Diabetes 2026, American Diabetes Association (2026)
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