Metabolic health
HbA1c: your blood sugar, averaged over three months
A finger-prick glucose is a single snapshot, high after lunch, low before breakfast. For most people HbA1c is the running average of your blood sugar over about three months, which is why it's the number used to judge diabetes risk.
Blood sugar is a moving target. It climbs after a meal, dips overnight, spikes with stress. So a single glucose reading tells you about one moment, which isn't much use for judging the bigger picture. HbA1c solves that by giving you an average.
Sugar that sticks
When there's glucose in your blood, a little of it sticks to the haemoglobin inside your red blood cells, and it stays stuck. Red cells live for about three months, so the amount of glued-on sugar builds a running record of how high your blood sugar has been. Measure it, and you get roughly a three-month average in a single number, weighted towards the most recent few weeks. No fasting required.
What your number means
As a guide: under 42 is the healthy range, 42 to 47 signals raised risk (sometimes called pre-diabetes), and 48 or above is in the diabetes range (Diabetes UK). Diagnosis is never one number in isolation: if you have no symptoms, a single result of 48 or above is not a diagnosis on its own and needs repeating before anything is concluded. Your doctor reads it alongside the rest of your picture.
Why HbA1c beats a one-off glucose
It responds to you
HbA1c isn't fixed. Losing a little weight, moving more, and cutting back on refined carbs can bring it down over a few months. And because it's an average, a genuine change shows up clearly rather than as daily noise.
When HbA1c can mislead
The three-month average only holds if your red blood cells are behaving normally, so there are situations where HbA1c is not a reliable guide and a different test is needed. That includes pregnancy, anaemia (particularly haemolytic anaemia, and also untreated iron or B12 deficiency), haemoglobin variants such as sickle cell trait or thalassaemia, recent blood transfusion, and advanced kidney disease. Anything that shortens red cell life tends to read falsely low; anything that lengthens it tends to read falsely high. UK guidance is clear that HbA1c should not be used to diagnose diabetes in these circumstances, or in suspected type 1 diabetes or rapid-onset symptoms, where a fasting glucose or an oral glucose tolerance test is used instead. This is one of the reasons a doctor reviews your result rather than a number simply landing in your inbox.
Who should check it
- You have a family history of type 2 diabetes
- You carry extra weight, especially around the middle
- You've been told your blood sugar was 'a bit high' once and never followed up
- You want an early, honest read on your metabolic health
An HbA1c of 48 mmol/mol (6.5%) or above is used to diagnose diabetes; 42 to 47 mmol/mol indicates a high risk of developing it.
UK diagnostic criteria for diabetes, Diabetes UK
HbA1c will be included in our metabolic and longevity panels when we open.
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