HbA1c
Glycated haemoglobin
HbA1c shows what proportion of your haemoglobin has sugar attached to it, which reflects average blood glucose over roughly the previous three months.
Reference range
%- Women
- 4–6 %
- Men
- 4–6 %
Reference ranges differ between laboratories and assays. Always read your result against the range printed on your own report.
What HbA1c measures
Glucose in the bloodstream attaches to haemoglobin in a slow, irreversible reaction. The higher the average glucose, the greater the share of haemoglobin that ends up glycated.
Red blood cells live about 120 days, so the measurement covers roughly that window — weighted towards the most recent weeks. A single high glucose reading says little; HbA1c cannot be talked around by one careful day before the appointment.
It is reported either as a percentage or in mmol/mol, depending on the laboratory. Both describe the same thing.
Why it gets tested
To diagnose and monitor diabetes and prediabetes, and increasingly as part of routine metabolic screening in people with risk factors such as raised BMI or a family history.
Commonly associated with low values
- Usually unremarkable
- Sometimes a shortened red cell lifespan, as in haemolytic anaemia or after significant blood loss
Commonly associated with high values
- Prediabetes or diabetes, depending on the threshold reached
- Insulin resistance developing over time
- Occasionally iron deficiency anaemia, which raises HbA1c without raising glucose
What can shift the result
- Anything that changes red cell lifespan distorts the result — anaemia, haemoglobin variants, recent transfusion, pregnancy
- Iron deficiency raises HbA1c independently of glucose, which is a common source of confusion
- Chronic kidney disease can shift it in either direction
Questions
Can HbA1c be wrong?
It can be misleading in specific situations. Because it depends on red blood cells surviving their normal lifespan, anything that shortens or lengthens that lifespan shifts the result — anaemia, haemoglobin variants, a recent transfusion or pregnancy. In those cases glucose is measured directly instead.
How far back does HbA1c look?
Roughly three months, but not evenly. The most recent four weeks contribute around half the value, so a genuine change in glucose control shows up sooner than people expect — though not within days.
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This page is general information about a laboratory value. It is not a diagnosis and does not replace medical advice. Discuss your own results with a doctor, who can read them in the context of your history and symptoms.