HbA1c Blood Test

• HbA1c (glycated haemoglobin) (measured): the proportion of haemoglobin with glucose attached, in mmol/mol. A percentage, if shown, is a conversion of the same result.

This test does not measure your glucose at the time of sampling or insulin. These are available as separate tests.

Glucose in the blood enters red cells and attaches slowly and permanently to haemoglobin, a process called glycation. The higher the average glucose, the larger the share of haemoglobin that becomes glycated. Because red cells circulate for a few months before being replaced, HbA1c acts as a record of average glucose; NICE describes it as reflecting the previous 8 to 12 weeks.

This link to red cells is both the test's strength and its main limitation. HbA1c smooths out the day-to-day swings that affect a single glucose reading, but anything that changes how long red cells survive, or the structure of haemoglobin, can move HbA1c independently of glucose.

UK laboratories report HbA1c in mmol/mol, aligned to the international (IFCC) reference method. In 2011 the World Health Organization advised that HbA1c can be used to diagnose diabetes, with a cut-off of 6.5% (48 mmol/mol), where assays are properly standardised and no interfering conditions are present. It also stated that a lower value does not exclude diabetes diagnosed using glucose tests.

The thresholds below are those used in UK guidance for adults. Your report also shows the laboratory's own reference range.

• Below 42 mmol/mol: below the range NICE uses to define high risk. NICE notes HbA1c is a continuous risk factor, so there is no single point where risk begins.
• 42 to 47 mmol/mol (6.0 to 6.4%): NICE guideline PH38 uses this range to indicate high risk of type 2 diabetes, sometimes called non-diabetic hyperglycaemia.
• 48 mmol/mol (6.5%) or above: the recommended cut-off for diagnosing diabetes. Without symptoms, a diagnosis should not rest on a single result; a repeat test is needed and diagnosis is made by a clinician.

When HbA1c can be misleading

UK guidance advises glucose-based testing instead of HbA1c in situations including:

• Haemoglobin variants such as sickle cell trait or thalassaemia (depending on the laboratory method)
• Iron deficiency, which may raise HbA1c; haemolysis or recent blood loss, which may lower it; and recent transfusion
• Kidney disease at stage 3b or beyond
• Pregnancy now or within the last two months
• Children and young people, suspected type 1 diabetes, or symptoms that came on quickly
• Recently started steroids or antipsychotics; HIV and some medicines such as certain antiretrovirals, ribavirin and dapsone
• Conditions that change red cell lifespan, such as an enlarged or removed spleen, or erythropoietin treatment

A result of 42 mmol/mol or above is worth sharing with your GP, who can confirm it and discuss NHS support. With your consent, we can write to your GP. Do not change any diabetes medicine because of this test.

Type 2 diabetes usually develops gradually and may cause few symptoms for some time. People commonly consider HbA1c when they have a family history of type 2 diabetes, a previous borderline result, or simply want to know where they stand. Eligible adults may also be offered diabetes risk checks through their GP practice, including the NHS Health Check.

People who may find it useful

• Adults with risk factors for type 2 diabetes who want to know their current level
• People tracking a result over time as part of a wider health review

When this test is not the right route

• Symptoms of high glucose such as marked thirst, passing urine much more often, unexplained weight loss or new tiredness, especially if they came on over days or weeks: contact your GP or NHS 111 the same day. HbA1c can miss a rapid rise.
• Diagnosed diabetes: monitoring belongs with your diabetes team, and medicines should never be adjusted on the basis of this test.
• Pregnancy, children and young people, and the situations listed under "Understanding your results".

Established clinical use

HbA1c is central to diabetes diagnosis and management in the UK. NICE recommends that people with an HbA1c of 42 to 47 mmol/mol are offered support with lifestyle change.

Population associations

In the US ARIC study of 11,092 adults without diabetes, higher HbA1c was associated with later diabetes, coronary heart disease and stroke, and more strongly with cardiovascular disease and death than fasting glucose. The link with death from any cause was J-shaped: the lowest values were also associated with higher risk.

How to read this evidence

These are population associations. They do not show that pushing HbA1c lower in people without diabetes lengthens life, and lower is not automatically better. HbA1c does not measure biological age; its value lies in identifying raised glucose early, when established prevention measures can help.

• Fasting: not required; any time of day is fine.
• Diet: changing what you eat for a few days beforehand will not meaningfully change the result.
• Tell us when booking about any haemoglobin variant, anaemia, kidney disease, recent transfusion or blood loss, pregnancy, and your medicines. Keep taking prescribed medicines as normal.

Choose how your sample is taken when you book. We confirm the collection option, any collection fee and the expected turnaround time before you book.

• Juvenology Clinic, Maidstone (82 King Street, Maidstone ME14 1BH): Available.
• Partner clinic near you, anywhere in the UK: Available on request. We confirm availability for your postcode before you book.
• Postal home finger-prick kit: Ask before ordering. We offer a home kit only where the laboratory confirms this test is suitable for a finger-prick sample.

Sample: Venous whole blood (EDTA tube)

Collection notes: No fasting needed and the sample can be taken at any time of day. Finger-prick collection may be possible for HbA1c, but a postal kit is offered only where the laboratory confirms its method is suitable for capillary samples. Tell us about any haemoglobin variant, anaemia, kidney disease, recent transfusion or pregnancy before booking.

The price of this test covers laboratory analysis and the laboratory's results report. The report lists each result beside the laboratory's reference range.

Beyond the blood test: optional support, priced separately

• Personalised written interpretation report: £50
• General consultation: £50
• Results consultation (results discussion and follow-up advice): £100
• Personalised programme: from £150, after we assess whether a programme suits you

Consultations are with Marina, an NMC-registered nurse. She explains what your results show and how they relate to lifestyle. No prescription service is offered with these tests.

If a result suggests you need medical follow-up, we will recommend that you see your GP and, with your consent, can provide a letter to take with you. A blood test cannot rule out every condition. If you have symptoms, speak to your GP or NHS 111, and call 999 in an emergency.

What is the difference between HbA1c and a glucose test?

A glucose test measures your level at the moment of sampling, usually after fasting. HbA1c reflects the average over about two to three months and needs no fasting. Each is preferred in different situations, and clinicians sometimes use both.

Can this test diagnose diabetes?

No test bought online gives a diagnosis on its own. A result of 48 mmol/mol or above without symptoms needs a repeat test, and diagnosis is made by your GP or another clinician.

I have sickle cell trait or thalassaemia. Should I use this test?

Haemoglobin variants can make HbA1c inaccurate, depending on the method. Please mention this before booking; a glucose-based test arranged with your GP may suit you better.

How often is it worth repeating?

HbA1c changes slowly, so repeating it within about three months usually adds little, unless a clinician needs to confirm a result in the diagnostic range.

Is interpretation included in the price?

The price covers laboratory analysis and the laboratory's report. You can add an optional personalised written interpretation report (£50) or book a results discussion consultation (£100).

1. Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus: abbreviated report of a WHO consultation. World Health Organization, 2011. https://www.ncbi.nlm.nih.gov/books/NBK304271/
2. Type 2 diabetes: prevention in people at high risk. NICE public health guideline PH38, 2012 (updated 2017). https://www.nice.org.uk/guidance/ph38
3. Diagnostic criteria for diabetes. Diabetes UK. https://www.diabetes.org.uk/About_us/What-we-say/Diagnosis-ongoing-management-monitoring/New_diagnostic_criteria_for_diabetes/
4. Consensus approach to the diagnosis of type 2 diabetes. London Diabetes Clinical Network, NHS England (London), 2018. https://www.england.nhs.uk/london/wp-content/uploads/sites/8/2019/07/dia-consensus-type2-27092018-FINAL.pdf
5. HbA1c test. Lab Tests Online UK (Association for Laboratory Medicine). https://labtestsonline.org.uk/tests/HBA1C-TEST
6. Selvin E, Steffes MW, Zhu H, et al. Glycated hemoglobin, diabetes, and cardiovascular risk in nondiabetic adults. New England Journal of Medicine, 2010;362(9):800-811. https://doi.org/10.1056/NEJMoa0908359