HbA1c is one of the most useful numbers in modern medicine — a single blood test that summarises how your blood sugar has behaved over the previous few months. It is the standard way doctors screen for type 2 diabetes and, just as importantly, for pre-diabetes: the in-between stage where levels are higher than they should be but not yet in the diabetic range. Understanding what the test measures makes it much easier to know what to do with the result.
What HbA1c actually measures
When there is glucose (sugar) in your bloodstream, a small amount of it sticks to haemoglobin, the protein inside your red blood cells that carries oxygen. The more sugar circulating over time, the more becomes attached. Because red blood cells live for around three months, measuring the proportion of "sugar-coated" haemoglobin gives an average picture of your blood sugar over that whole period.
This is what makes HbA1c so practical. Unlike a finger-prick or fasting glucose reading, which only captures a single moment, HbA1c is not thrown off by what you ate this morning or whether you skipped breakfast. It reflects the bigger trend, so you do not need to fast beforehand.
Understanding the ranges
HbA1c is reported in mmol/mol. As a broad guide used across the UK:
- Below 42 mmol/mol — considered within the normal range.
- 42 to 47 mmol/mol — the pre-diabetes range, sometimes called non-diabetic hyperglycaemia.
- 48 mmol/mol or above — in the range used to diagnose type 2 diabetes, usually confirmed with a repeat test.
These figures are a general reference rather than a personal verdict. A single borderline result is always interpreted alongside your symptoms, risk factors and, where needed, a repeat test.
Why pre-diabetes matters
Pre-diabetes means your body is starting to struggle to keep blood sugar in check, often because of insulin resistance. Left unaddressed, a meaningful proportion of people go on to develop type 2 diabetes within a few years. The good news is that this stage is frequently reversible. Modest, sustained changes — losing a little weight if you carry extra, moving more, cutting back on sugary drinks and refined carbohydrates — can bring HbA1c back down and delay or prevent diabetes altogether.
Check your HbA1c
An HbA1c test screens for pre-diabetes and type 2 diabetes.
Book an HbA1c testWho should consider testing
It is worth checking your HbA1c if you carry extra weight around the middle, have a family history of type 2 diabetes, have high blood pressure or raised cholesterol, or belong to an ethnic group with higher risk. Symptoms such as increased thirst, needing to pass urine more often, or unexplained tiredness are also good reasons to test — though many people with early changes have no symptoms at all, which is exactly why screening is helpful.
What to do with your result
A normal result is reassuring and gives you a baseline to compare against in future. A pre-diabetes result is an opportunity: it flags a risk while there is still plenty you can do about it, and a doctor can help you build a plan and arrange a follow-up test to track your progress. A result in the diabetes range should always be discussed with a clinician, who will confirm it and guide next steps.
Check your HbA1c
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Specialist interest: Cardiovascular Medicine · OneMedicine, CQC-registered clinic