Single marker guide · HbA1c (glycated haemoglobin)
HbA1c is your average blood sugar over the last three months, and it is the test the NHS uses to diagnose diabetes. It is a good test for that. What it is bad at is warning you early: insulin resistance runs for ten to fifteen years before HbA1c leaves the normal range, and by the time it reads 42 the metabolic problem is well established. Here is what the number means, the UK thresholds, the people it misreads, and the markers that see the same problem a decade sooner.
Venous draw at 103 UK clinics or at home. UKAS-accredited laboratory. Report reviewed by a medical professional.
The short answer
Glucose in the blood sticks to haemoglobin in red cells, and because red cells live about three months, the proportion of haemoglobin with glucose attached, HbA1c, reflects your average blood sugar over that period. It smooths out the day-to-day noise of a single glucose reading, it does not need fasting, and it is the basis for diagnosing diabetes and prediabetes in the UK. For those jobs it is the right test.
The limitation is what it cannot see. In the years before diabetes, the body keeps blood sugar normal by producing more and more insulin. HbA1c stays in range the whole time, because the sugar is being controlled; it is the effort required to control it that is climbing. That effort is measured by fasting insulin and HOMA-IR, and it goes wrong a decade before HbA1c does. Someone with an HbA1c of 38 and a fasting insulin of 120 pmol/L is not healthy; they are five years from prediabetes and nobody has told them. That is why we test HbA1c alongside insulin, never alone. Prediabetes and insulin resistance guide.
Reference ranges
| HbA1c (mmol/mol) | HbA1c (%) | Category | What it means |
|---|---|---|---|
| Below 36 | Below 5.4 | Optimal | Where metabolically healthy adults sit. Preventive clinicians aim here rather than merely under 42. |
| 36 to 41 | 5.4 to 5.9 | Normal | Inside the NHS normal range, but the upper half of it is where fasting insulin is often already raised. The trend from year to year matters here. |
| 42 to 47 | 6.0 to 6.4 | Prediabetes | Non-diabetic hyperglycaemia. Around one in three people in this range develop type 2 diabetes within five years without change; most who act do not. Eligible for the free NHS Diabetes Prevention Programme. |
| 48 and above | 6.5 and above | Diabetes | Diagnostic threshold, confirmed by a repeat test. Type 2 diabetes caught at this level is often reversible with sufficient weight loss, which is a reason to test rather than avoid it. |
| Above 58 | Above 7.5 | Poorly controlled | In a known diabetic, above the usual treatment target; complications risk rises steeply from here. GP review. |
The UK reports HbA1c in mmol/mol (IFCC units); older results and most other countries use percentages. To convert, 42 mmol/mol is 6.0%, 48 is 6.5%, 53 is 7.0%, and each 11 mmol/mol is roughly one percentage point. TrueVitals reports show both units and the risk-based targets.
Where it misreads
Because the test measures glucose stuck to haemoglobin, it assumes your red cells are normal and live a normal length of time. In a surprising number of people that is not true, and the result reads wrong in a direction that is easy to miss without the other markers in the panel.
Low iron makes red cells live longer, so more glucose accumulates on them. A ferritin of 15 can push HbA1c up by 2 to 4 mmol/mol, enough to tip a normal result into prediabetes. Correcting the iron brings it back down. This is one reason ferritin and HbA1c belong in the same draw. Ferritin guide.
Sickle cell trait, thalassaemia trait and other variants, common in people of African, Caribbean, South Asian and Mediterranean heritage, can make HbA1c unreliable. The full blood count flags the pattern, and fasting glucose and insulin give a reading that does not depend on haemoglobin.
Anything that shortens red cell life, heavy periods, a bleed, haemolysis, a recent transfusion, replaces old glucose-laden cells with new clean ones and lowers HbA1c below your true average.
Both alter red cell turnover and can shift HbA1c in either direction. The kidney and liver markers in every panel show whether this applies to you. Kidney function guide.
HbA1c falls in pregnancy as red cell turnover rises, which is why gestational diabetes is diagnosed with a glucose tolerance test instead.
HbA1c drifts up slightly with age independent of glucose, and high-dose vitamin C or E can lower it. Neither is large, but both are worth knowing about at the margins of a category.
Who should test
The NHS Health Check only tests HbA1c if a risk score flags you, which means most people under 40 have never had one. The case for a baseline is strong for anyone with a waist over 94 cm (men) or 80 cm (women), a parent or sibling with type 2 diabetes, South Asian, Black African or Caribbean heritage, a history of gestational diabetes or PCOS, high blood pressure, or a fatty liver. The case for testing it beside fasting insulin is strongest in exactly the people HbA1c misreads and exactly the people with years of insulin resistance still to run. Diabetes blood test guide.PCOS blood test guide.
Read it in context
HbA1c tells you your average blood sugar. The markers beside it tell you how hard your body is working to achieve it, whether the number is trustworthy, and what it is costing your heart and liver.
The early warning. Insulin resistance shows here 10 to 15 years before HbA1c moves, while it is fully reversible. A normal HbA1c with a HOMA-IR above 2 is the most common metabolic finding in a healthy-looking 40-year-old. In Ultimate.
A single-moment reading that does not depend on red cells. When HbA1c and fasting glucose disagree, one of the misreads above is usually the reason. In every panel.
The two checks on whether HbA1c can be trusted. Low ferritin inflates it; a variant or anaemia distorts it. Both in every panel.
High triglycerides with low HDL is the lipid fingerprint of insulin resistance, and it drives the small, dense ApoB particles that cause heart disease. Metabolic and cardiovascular risk are one problem seen from two sides. ApoB guide.
A fatty liver is both cause and consequence of insulin resistance, and it is present in most people with prediabetes. Raised ALT or GGT next to a borderline HbA1c points to the liver as the place to start. Liver guide.
Inflammation and uric acid both rise with insulin resistance and both raise cardiovascular risk independently. Seeing them alongside HbA1c completes the metabolic syndrome picture. hs-CRP guide.
Which test
Advanced
74 biomarkers · £269
HbA1c and fasting glucose with triglycerides, HDL, ApoB, liver enzymes, hs-CRP, uric acid, ferritin and a full blood count. The checks on HbA1c and the consequences of it, in one draw.
View AdvancedIncludes insulin + HOMA-IR
Ultimate
114 biomarkers · £349
Everything in Advanced plus fasting insulin, HOMA-IR and C-peptide, the markers that show insulin resistance a decade before HbA1c, with Lp(a), cystatin C and complete hormones.
View UltimateSignature
230 biomarkers · £799
Processed by Randox. A full metabolic syndrome profile with extended cardiovascular, liver and inflammatory markers, plus physical measurements including waist and blood pressure.
View SignatureClinic draw £19 at 103 UK clinics. At-home phlebotomist £39 across 200+ areas. Fast from 10pm the night before. Pay monthly available.
Honest comparison
If you have diagnosed diabetes or prediabetes, your GP should be testing HbA1c every three to six months, free, and that is the right route. If you have a recent full panel and simply want to see whether three months of changes have moved your average, a standalone HbA1c from Medichecks costs around £39 and does the job. Pharmacies also offer finger-prick HbA1c for a similar price.
A panel is the better choice for a first look, because a normal HbA1c on its own is exactly the result that gives false reassurance. It cannot show insulin resistance, it cannot tell you whether low iron or a haemoglobin variant is distorting it, and it cannot show what blood sugar is doing to your liver and your arteries. Those are the answers that decide what you change. See how every UK provider compares.
After the result
Metabolically healthy. Retest annually to watch the trend; a steady climb inside the normal range is the earliest signal you will get.
The window that matters. Insulin resistance at this stage reverses with less refined carbohydrate, more protein and fibre, resistance training, sleep and a modest loss of visceral fat, typically within three to six months. Your report tells you which of these apply and sets a retest date.
Take your report to your GP. 42 to 47 qualifies you for the free NHS Diabetes Prevention Programme, and 48 or above needs a confirmatory repeat and a diagnosis, which unlocks structured support and, for many, the chance of remission through weight loss. Check ferritin first: if it is low, some of the number may be iron, not sugar.
This page is general information, not medical advice. Excessive thirst, frequent urination, blurred vision or rapid unexplained weight loss need a GP appointment promptly.
FAQs
The percentage of haemoglobin in your red cells that has glucose attached, which reflects your average blood sugar over the previous two to three months, weighted towards the most recent month. It is reported in mmol/mol in the UK and as a percentage elsewhere.
Below 42 mmol/mol (6.0%) is normal, 42 to 47 (6.0 to 6.4%) is prediabetes, and 48 (6.5%) or above indicates diabetes. Preventive clinicians generally consider below 36 mmol/mol optimal. TrueVitals reports show both units and both sets of thresholds.
Not for HbA1c itself; it reflects three months, not this morning. TrueVitals panels also include fasting glucose, insulin and triglycerides, so we ask you to fast from 10pm the night before and drink water as normal.
Yes, in specific situations. Iron deficiency raises it falsely, blood loss and anaemia lower it, haemoglobin variants such as sickle cell or thalassaemia trait distort it, and pregnancy and kidney disease alter it. Fasting glucose and a full blood count in the same panel show whether any of these apply to you.
Because your body is keeping blood sugar normal by producing extra insulin. That is insulin resistance, and it precedes a rise in HbA1c by a decade or more. It is the most reversible stage of the process and the reason fasting insulin and HOMA-IR are worth testing alongside HbA1c.
Because it reflects three months, meaningful change takes about that long to show fully, though a determined change in diet and activity can drop it by 5 to 10 mmol/mol in a single cycle. Retest at three months to see the effect of what you have changed.
Yes if you have symptoms, a risk factor your GP recognises, or a high score at an NHS Health Check. Routine testing under 40 without those is uncommon. A private panel includes it as standard. What to ask your GP for.
A standalone HbA1c is around £39. A TrueVitals Advanced panel is £269 and includes HbA1c with fasting glucose, lipids, ApoB, liver, ferritin and 65 other markers; Ultimate at £349 adds fasting insulin, HOMA-IR and C-peptide, the markers that see insulin resistance before HbA1c does.
74 to 230 biomarkers. Venous draw at 103 UK clinics or at home. A report that tells you what your results mean and what to do next.
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