What A1c Is Prediabetes? UK HbA1c Guide

Understanding what A1c level indicates prediabetes is an important step in protecting your long-term health. In the UK, prediabetes is identified using the HbA1c blood test, with a reading of 42 to 47 mmol/mol (approximately 6.0% to 6.4%) placing you in the non-diabetic hyperglycaemia range. This means your blood glucose is higher than normal but not yet at the threshold for a type 2 diabetes diagnosis. Recognising this early gives you a genuine opportunity to make changes that can bring your levels back to normal and significantly reduce your risk of developing diabetes.

What HbA1c level means you have prediabetes in the UK?

An HbA1c of 42 to 47 mmol/mol indicates prediabetes in the UK, per NICE guidance PH38. This sits above the normal upper limit of 41 mmol/mol but below the 48 mmol/mol threshold for type 2 diabetes.

In the UK, an HbA1c reading of 42 to 47 mmol/mol (6.0% to 6.4% in older percentage units) indicates prediabetes, also called non-diabetic hyperglycaemia (NDH). This range sits above the normal upper limit of 41 mmol/mol but below the threshold of 48 mmol/mol at which type 2 diabetes is diagnosed. These thresholds are set out in NICE public health guidance on type 2 diabetes prevention in people at high risk (PH38) and are used to identify people who may benefit from early intervention through programmes such as the NHS Diabetes Prevention Programme. Local laboratory reference ranges may vary slightly, so it is always worth reading the comment on your own result or discussing it with your GP.

HbA1c stands for glycated haemoglobin. It reflects the average blood glucose level over the preceding two to three months, because glucose attaches to haemoglobin in red blood cells at a rate proportional to how much glucose is circulating.^[4][16] This makes it a more reliable indicator of longer-term blood sugar control than a single fasting glucose reading.

HbA1c is reported in mmol/mol in UK laboratories, following the International Federation of Clinical Chemistry (IFCC) standard adopted in 2011. Older percentage values (DCCT units) are still sometimes quoted in patient-facing materials, so it is helpful to know that 42 mmol/mol corresponds to approximately 6.0% and 47 mmol/mol to approximately 6.4%. If you receive a result, check which unit your laboratory has used to avoid confusion.

How is an HbA1c test carried out and what do the results mean?

HbA1c is a simple, non-fasting blood test reported in mmol/mol; results below 42 are normal, 42 to 47 indicate prediabetes, and 48 or above suggest type 2 diabetes requiring confirmatory testing.

An HbA1c test is a simple blood test, usually taken from a vein in the arm at a GP surgery or NHS laboratory, and it does not require fasting beforehand. A small blood sample is sent to a laboratory where the proportion of haemoglobin that has glucose attached is measured. Results are typically available within a few days and are reported in mmol/mol.

The results are interpreted as follows:

• Below 42 mmol/mol: Normal range, no evidence of prediabetes or diabetes.

• 42 to 47 mmol/mol: Prediabetes (non-diabetic hyperglycaemia), indicating elevated risk.

• 48 mmol/mol or above: Consistent with a diagnosis of type 2 diabetes. In the absence of symptoms, a second confirmatory test is usually required before a diagnosis is made, in line with UK diagnostic guidance.^[5][6]

Certain conditions can affect the reliability of HbA1c results. Haemolytic anaemia, iron deficiency anaemia, haemoglobin variants (such as sickle cell trait), and recent blood transfusions can all cause falsely low or falsely high readings.^[17][16] HbA1c is also less reliable during pregnancy and in people with advanced chronic kidney disease; in these circumstances, a fasting plasma glucose or an oral glucose tolerance test is generally preferred.^[14][15] If any of these factors apply, a GP may request an alternative test to confirm the picture.

HbA1c testing is also used to monitor people already identified as having prediabetes, typically every six to twelve months, to assess whether lifestyle changes are having a beneficial effect or whether blood glucose is rising towards the diabetic range. Your GP or practice nurse will advise on the interval most appropriate for your situation.

What are the symptoms and risk factors for prediabetes?

Prediabetes typically causes no symptoms, so screening is essential. Key risk factors include excess weight, physical inactivity, age over 40, family history of type 2 diabetes, and previous gestational diabetes.

Prediabetes usually causes no noticeable symptoms, which is why many people are only identified through routine blood tests or NHS Health Checks. Because blood glucose is elevated but not yet at diabetic levels, the body has not yet reached the point where classic symptoms such as excessive thirst, frequent urination, or unexplained fatigue become prominent. This absence of symptoms makes opportunistic screening particularly important.

Several well-established risk factors increase the likelihood of having prediabetes:

• Excess weight, particularly abdominal (central) obesity, which increases insulin resistance. For South Asian, Chinese, and other high-risk ethnic groups, lower BMI thresholds apply in UK guidance (overweight defined as BMI 23 kg/m2 or above, obesity as 27.5 kg/m2 or above).

• Physical inactivity, as regular exercise helps the body use insulin more effectively.

• Age over 40 (or over 25 in people of South Asian, Black African, or Black Caribbean heritage, who are at higher risk at a younger age, as set out in NICE prevention guidance PH38).^[1][2]

• Family history of type 2 diabetes in a first-degree relative.

• Previous gestational diabetes during pregnancy.

• Polycystic ovary syndrome (PCOS), which is associated with insulin resistance.

• Certain medicines, including long-term corticosteroids and some antipsychotics.

• High blood pressure or raised cholesterol, which often cluster with insulin resistance.

The NHS Health Check programme, offered to adults aged 40 to 74 in England every five years, includes an assessment of diabetes risk and may prompt an HbA1c test.^[10] People with known risk factors are encouraged to take up this offer. Identifying prediabetes early creates a meaningful window for intervention before type 2 diabetes develops.

Can prediabetes be reversed, and how quickly?

Prediabetes can be reversed through sustained lifestyle changes, with some people seeing HbA1c improvements within three to six months, though underlying susceptibility remains and ongoing monitoring is recommended.

Prediabetes can be reversed in many people, with HbA1c returning to the normal range through sustained lifestyle changes, though the speed and extent of improvement vary between individuals. Evidence from randomised controlled trials and NHS Diabetes Prevention Programme evaluations indicates that structured lifestyle intervention can meaningfully reduce the risk of progression to type 2 diabetes in people with non-diabetic hyperglycaemia, though the precise effect size varies across studies and individual outcomes depend on starting HbA1c, body weight, age, and adherence to changes.

Some people see measurable improvements in HbA1c within three to six months of making consistent dietary and physical activity changes, particularly if weight loss is achieved. This reflects the two to three month window that HbA1c captures, based on the lifespan of red blood cells. However, reversal is not guaranteed, and for some individuals the underlying tendency towards insulin resistance means that blood glucose levels may rise again if lifestyle changes are not maintained long term.

It is important to understand that "reversal" in this context means returning HbA1c to the normal range, not eliminating the underlying susceptibility. People who have had prediabetes remain at higher lifetime risk of developing type 2 diabetes compared with those who have never had elevated readings, and ongoing monitoring is recommended even after normalisation.

For people who do not achieve sufficient improvement through lifestyle changes alone, or whose HbA1c is at the higher end of the prediabetes range, a GP may discuss whether additional support or medication is appropriate. NICE prevention guidance (PH38) sets out the specific circumstances in which metformin may be considered for people at high risk, though lifestyle intervention remains the first-line approach and metformin is not routinely prescribed for prediabetes in the UK outside specialist settings.^[1][2]

What treatments and lifestyle changes does the NHS recommend?

The NHS recommends dietary change, at least 150 minutes of moderate activity per week, and weight management; the free NHS Diabetes Prevention Programme offers structured support to eligible adults.

The NHS recommends a combination of dietary change, increased physical activity, and weight management as the primary approach for people with prediabetes. The NHS Diabetes Prevention Programme (NHS DPP), commissioned by NHS England, offers a free structured behaviour change programme to eligible adults with non-diabetic hyperglycaemia. The programme typically runs over nine months and includes group or digital sessions covering healthy eating, physical activity, and psychological support for behaviour change.

Key lifestyle recommendations aligned with NICE guidance include:

• Dietary changes: Reducing intake of refined carbohydrates and added sugars, increasing fibre from vegetables, pulses, and wholegrains, and moderating overall calorie intake to support weight loss where appropriate.

• Physical activity: Aiming for at least 150 minutes of moderate-intensity aerobic activity per week (such as brisk walking or cycling), alongside muscle-strengthening activities on two or more days per week, in line with the UK Chief Medical Officers' Physical Activity Guidelines.

• Weight management: Even modest weight loss of 5% to 10% of body weight can meaningfully improve insulin sensitivity and lower HbA1c.

• Alcohol: Keeping within the UK Chief Medical Officers' low-risk guidelines of no more than 14 units per week, spread across several days.^[13]

• Smoking cessation: Smoking worsens insulin resistance and cardiovascular risk; NHS Stop Smoking services are available free of charge.

For people seeking additional support with weight management as part of their prediabetes care, a GP can discuss all available options. Bolt Pharmacy is a GPhC-registered UK online pharmacy (GPhC registration covers Great Britain; patients in Northern Ireland should check with the Pharmaceutical Society of Northern Ireland) offering online weight-management consultations, with prescriber review and pharmacist support, where clinically appropriate options may be considered following consultation. Referral to a dietitian or specialist weight management service through the NHS is also available for those who meet local criteria, with decisions made by the relevant Integrated Care Board.

When should you see your GP about your blood sugar levels?

See your GP if your HbA1c is in the prediabetes range, if you have multiple risk factors, or if you develop symptoms such as increased thirst, frequent urination, or unexplained fatigue.

You should see your GP if you have received an HbA1c result in the prediabetes range (42 to 47 mmol/mol), if you have not had a blood sugar test but have several risk factors for type 2 diabetes, or if you notice symptoms that could suggest blood glucose is rising, such as increased thirst, passing urine more frequently than usual, unexplained fatigue, or blurred vision. These symptoms warrant prompt assessment rather than waiting for a routine appointment.

If you have already been told you have prediabetes, your GP or practice nurse should arrange follow-up HbA1c testing, typically every six to twelve months, to monitor whether your levels are improving, stable, or progressing. Missing these reviews means that a rise into the diabetic range could go undetected.

Contact your GP promptly (rather than waiting) if:

• Your HbA1c result is at the upper end of the prediabetes range (close to 47 mmol/mol) or has risen since your last test.

• You develop symptoms of diabetes, including extreme thirst, frequent urination, or unintentional weight loss.

• You are pregnant or planning a pregnancy, as blood glucose targets and monitoring requirements differ during pregnancy. Note that HbA1c is not the preferred test for diagnosing gestational diabetes; an oral glucose tolerance test (OGTT) is used in line with UK practice.

• You are taking a medicine known to raise blood glucose, such as a corticosteroid, and have not had a recent HbA1c check.

For urgent concerns outside GP hours, NHS 111 can provide advice. If you experience symptoms of diabetic ketoacidosis (such as vomiting, abdominal pain, rapid breathing, or confusion), call 999 or go to A&E immediately, as this is a medical emergency. Suspected side effects from any medicine can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Scientific References

1. Type 2 diabetes: prevention in people at high risk (PH38) – Recommendations.
2. Type 2 diabetes: prevention in people at high risk (PH38).
3. Type 2 diabetes: prevention in people at high risk (PH38) – PDF.
4. Diabetes.
5. Type 2 diabetes in adults: management (NG28) – Blood glucose management.
6. Type 2 diabetes in adults: management (NG28) – Recommendations.
7. Appendix A1: Summary of evidence from surveillance (NG246).
8. Referring people at high risk of type 2 diabetes (QS167).
9. Diabetes: IFCC-HbA1c 75 mmol/mol or less – Indicator IND136.
10. NHS Health Check.
11. UK Chief Medical Officers' physical activity guidelines.
12. Physical activity guidelines for adults aged 19 to 64.
13. Alcohol consumption: advice on low risk drinking – UK Chief Medical Officers.
14. Diabetes in pregnancy: management from preconception to the postnatal period (NG3) – Recommendations.
15. Diabetes in pregnancy: management from preconception to the postnatal period (NG3).
16. Diabetes | Treatment summaries – BNF.
17. A Rare Hemoglobin Variant Detected for the First Time in Türkiye (Hb Iraq-Halabja): Evaluation of the Effect of Variant Hemoglobins on HbA1c Methods.

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