If you have diabetes or prediabetes, your HbA1c is probably the number your GP talks about most. But what does it actually measure, how reliable is it, and what should you do with the result? Here is a clear, plain-English guide.
What HbA1c Measures
HbA1c — haemoglobin A1c, also called glycated haemoglobin — measures the percentage of haemoglobin (the protein in red blood cells) that has glucose attached to it. Because red blood cells live for roughly 10–12 weeks, HbA1c reflects your average blood sugar over approximately the past three months. Unlike a finger-prick test that shows a single moment in time, HbA1c gives a longer-term picture of control.
What the Numbers Mean
- Below 42 mmol/mol (6%): Normal — no diabetes
- 42–47 mmol/mol (6.0–6.4%): Prediabetes — increased risk; lifestyle intervention is highly effective here
- 48 mmol/mol (6.5%) or above: Diabetes — on two separate occasions for a formal diagnosis
- Target for most people with type 2 diabetes: 48–53 mmol/mol (6.5–7%), though individual targets vary
Limitations to Be Aware Of
HbA1c is not perfect. It can give misleading results in people with certain anaemias, haemoglobin variants (more common in some ethnic groups), or kidney disease. Pregnancy also affects the reading. If your GP suspects these factors may apply, they may use alternative tests such as fructosamine or continuous glucose monitoring.
How Often Should You Be Tested?
- If you have diabetes: typically every 3–6 months, depending on how well controlled your levels are
- If you have prediabetes: annually, or every 6 months if you are making active lifestyle changes
- If you are at risk (overweight, family history, over 40): discuss testing frequency with your GP
