Average blood glucose over roughly 2–3 months; key diabetes monitoring test.
What it is
Reported in mmol/mol (IFCC). Older % units appear on some overseas reports. Conditions shortening red-cell lifespan can distort HbA1c.
HbA1c reflects non-enzymatic glycation of haemoglobin over roughly the red-cell lifespan (about 2–3 months). UK labs report mmol/mol. Clinicians use it with history and other tests when assessing long-term glucose control.
Why it matters
Laboratories report HbA1c against their own reference intervals. UK clinical guidelines use defined cut-offs when diagnosing diabetes; only a qualified clinician can interpret your result in that context.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
Glucose attaches to haemoglobin over the red cell’s life; HbA1c approximates that exposure. It does not show day-to-day hypos or spikes.
Higher average glucose → more glycation → higher HbA1c. Glycation also affects other proteins (advanced glycation end-products) implicated in long-term diabetes complications.
For athletes
Useful season-average for athletes with diabetes under specialist care. Anaemia and haemoglobinopathies can mislead: tell the lab/clinician your sport and health history.
Useful as a season-average under specialist care. Anaemia, haemoglobin variants, and recent blood loss distort HbA1c: tell clinicians your sport and any altitude or donation history.
