Glycated haemoglobin HbA1c 6.0% is considered abnormal under NHS and NICE diagnostic criteria, placing it at the lower boundary of the non-diabetic hyperglycaemia (NDH) range — equivalent to 42 mmol/mol. This result does not mean you have diabetes, but it does indicate that blood glucose is higher than ideal and warrants attention. Understanding what this reading means, what can influence it, and what steps to take next is essential for protecting your long-term health. This article explains the NHS thresholds, factors that affect HbA1c accuracy, and the evidence-based actions recommended by NICE to help reduce your risk of developing type 2 diabetes.

What Does an HbA1c of 6.0% Mean on NHS Blood Tests?

An HbA1c of 6.0% (42 mmol/mol) meets the NICE threshold for non-diabetic hyperglycaemia, sitting at the lower boundary of the NDH range; it is not a diagnosis of diabetes but indicates blood glucose is higher than ideal.

HbA1c, or glycated haemoglobin, is a blood test used widely across the NHS to assess average blood glucose levels over the preceding two to three months. When glucose circulates in the bloodstream, it binds to haemoglobin — the protein inside red blood cells — forming glycated haemoglobin. The higher the blood glucose over time, the higher the HbA1c reading. This makes it a reliable long-term marker of glucose control, unlike a single fasting glucose measurement.

In the UK, HbA1c results are most commonly reported in millimoles per mole (mmol/mol), though some laboratories and older records may still use the percentage (%) format. An HbA1c of 6.0% is equivalent to approximately 42 mmol/mol (based on the IFCC–NGSP conversion used in UK laboratories).

According to NICE guidance (NG28) and NHS diagnostic criteria, an HbA1c of 42 mmol/mol (6.0%) meets the threshold for non-diabetic hyperglycaemia (NDH) — sometimes referred to informally as prediabetes. The NDH range is 42–47 mmol/mol (6.0–6.4%). A result of 42 mmol/mol therefore sits at the lower boundary of this range, not at the upper limit of normal. Below 42 mmol/mol is considered low risk. This distinction matters: a result of 6.0% does not mean a person has diabetes, but it does indicate that blood glucose is higher than ideal and warrants attention. Without lifestyle intervention, there is an increased risk of progressing to type 2 diabetes.

Important: when HbA1c should not be used for diagnosis HbA1c is not appropriate for diagnosing diabetes or NDH in all situations. It should not be used in:

• Pregnancy (including for diagnosing gestational diabetes — a 75 g oral glucose tolerance test (OGTT) is used instead, per NICE NG3)

• Children and young people

• Individuals with suspected type 1 diabetes

• People who have had symptoms for fewer than two months

• Conditions that affect red cell turnover or haemoglobin structure (such as haemolytic anaemia, haemoglobinopathies, or recent blood transfusion)

In these circumstances, fasting plasma glucose or an OGTT is the appropriate alternative. Your GP will advise which test is most suitable for you.

Understanding Normal and Abnormal HbA1c Ranges in the UK

NICE defines below 42 mmol/mol as low risk, 42–47 mmol/mol as non-diabetic hyperglycaemia, and 48 mmol/mol or above as diagnostic of type 2 diabetes; clinical interpretation should follow NICE thresholds rather than laboratory-specific reference ranges alone.

The NHS and NICE use clearly defined thresholds to interpret HbA1c results in clinical practice. These thresholds help clinicians categorise a patient's glucose status and guide further management:

• Low risk (normal): Below 42 mmol/mol (below 6.0%)

• Non-diabetic hyperglycaemia (NDH) / prediabetes: 42–47 mmol/mol (6.0–6.4%)

• Diagnostic of type 2 diabetes: 48 mmol/mol (6.5%) or above, confirmed on a repeat test in asymptomatic individuals

An HbA1c of exactly 6.0% (42 mmol/mol) sits at the lower boundary of the NDH range. Whether a laboratory flags this as 'abnormal' depends on the specific reference range used by that laboratory — some labs set their upper limit of normal at 41 mmol/mol, meaning 42 mmol/mol would appear outside the normal range on the printed report, marked with an asterisk or 'H' (high) flag. This can understandably cause concern. Regardless of how an individual laboratory report is formatted, clinical interpretation should follow NICE thresholds rather than laboratory-specific reference ranges alone.

When HbA1c is not a reliable test (see above), fasting plasma glucose or an OGTT should be used instead.

It is also worth noting that these thresholds are not absolute cut-offs representing a sudden change in biological risk — rather, they are clinically agreed boundaries designed to guide decision-making. A result of 42 mmol/mol does not carry the same clinical significance as a result of 47 mmol/mol, even though both fall within the same category. Context matters enormously, and a single result should always be interpreted alongside a patient's full clinical picture, including their weight, family history, ethnicity, and cardiovascular risk factors.

Conditions and Factors That Can Affect HbA1c Results

Iron deficiency anaemia, haemolytic anaemia, haemoglobin variants, recent blood transfusion, advanced CKD, and certain medicines — including corticosteroids and atypical antipsychotics — can all falsely raise or lower HbA1c results.

While HbA1c is a robust and widely validated test, several physiological and pathological factors can influence its accuracy, leading to results that may be falsely elevated or falsely lowered. Clinicians are trained to consider these variables when interpreting results.

Factors that may falsely raise HbA1c:

• Iron deficiency anaemia (reduced red cell turnover, prolonging red cell lifespan)

• Vitamin B12 or folate deficiency

• Splenectomy (prolonged red cell lifespan)

• Certain haemoglobin variants (depending on the assay used)

Factors that may falsely lower HbA1c:

• Haemolytic anaemia (shortened red cell lifespan)

• Recent blood transfusion

• Pregnancy (particularly the second and third trimesters) — note that HbA1c should not be used to diagnose gestational diabetes; a 75 g OGTT is recommended (NICE NG3)

• Advanced chronic kidney disease (CKD) or erythropoietin therapy, which can shorten red cell survival and lower HbA1c; assay interference may also occur depending on the method used

A note on haemoglobin variants and CKD: Haemoglobin variants (such as HbS in sickle cell trait, or HbC) can cause falsely high or falsely low HbA1c results depending on the specific assay used by the laboratory. The direction of interference cannot be generalised — if you have a known haemoglobin variant, your laboratory or GP can advise on the reliability of your result. In advanced CKD, HbA1c is frequently lower than expected due to shortened red cell survival and, where applicable, the effects of erythropoietin therapy; assay-specific interference may also occur. In individuals where HbA1c is unreliable, alternative tests such as fructosamine or an OGTT may be more appropriate.

UK laboratories follow IFCC standardisation and participate in UK NEQAS (National External Quality Assessment Service) external quality assurance programmes to ensure consistent and accurate HbA1c measurement. If you have concerns about a specific result, your GP can liaise with the laboratory.

Beyond medical conditions, lifestyle factors also influence HbA1c. A diet consistently high in refined carbohydrates and sugars, physical inactivity, and excess body weight — particularly central adiposity — may all contribute to a mildly elevated result. Psychological stress may also affect blood glucose through hormonal pathways, though the evidence for a direct effect on HbA1c in the general population is less clear-cut.

Certain medicines are known to raise blood glucose and consequently HbA1c, including systemic corticosteroids, atypical antipsychotics (such as olanzapine and clozapine), and some immunosuppressants (such as tacrolimus). If you are taking any of these medicines, your GP will take this into account when reviewing your result. Do not stop or alter any prescribed medicine without first seeking medical advice. If you think a medicine may be affecting your blood glucose, speak to your GP or pharmacist. Suspected side effects from medicines can also be reported via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk.

Next Steps If Your HbA1c Result Is Flagged as Abnormal

An HbA1c of 6.0% is manageable with lifestyle changes; NICE recommends annual monitoring for NDH, and eligible individuals can be referred to the NHS Diabetes Prevention Programme for structured dietary, physical activity, and behaviour change support.

Receiving a result flagged as abnormal can feel alarming, but an HbA1c of 6.0% is not a diagnosis of diabetes, and in many cases it is entirely manageable with targeted lifestyle changes. The NHS Diabetes Prevention Programme (NHS DPP), also known as Healthier You, is a nationally commissioned, evidence-based programme specifically designed for people with non-diabetic hyperglycaemia. Eligible individuals are referred by their GP and offered structured support including dietary advice, physical activity guidance, and behaviour change coaching.

UK evaluation data for the NHS DPP suggest that participation can reduce the risk of developing type 2 diabetes by around a third in high-risk individuals. Key evidence-based steps that can help bring HbA1c back within the low-risk range include:

• Dietary modification: Reducing intake of refined carbohydrates, sugary drinks, and ultra-processed foods; increasing fibre, vegetables, and wholegrains

• Regular physical activity: Aiming for at least 150 minutes of moderate-intensity exercise per week, as recommended by the UK Chief Medical Officers' Physical Activity Guidelines (2019)

• Weight management: Even a modest reduction of 5–10% of body weight can significantly improve insulin sensitivity

• Smoking cessation: Smoking is associated with insulin resistance and worsens glycaemic control

• Alcohol reduction: Excess alcohol contributes to weight gain and can impair glucose metabolism

Your GP or practice nurse will typically arrange a repeat HbA1c test to monitor whether your levels are improving, stable, or rising. NICE recommends that people with NDH have their HbA1c checked at least annually; your clinician may arrange an earlier review — for example at three to six months — to assess the impact of any lifestyle changes. This follow-up is an important part of ongoing care and should not be missed.

In some cases, additional investigations — such as a fasting glucose, lipid profile, or kidney function tests — may be requested to build a fuller picture of metabolic health. Do not stop or change any prescribed medicines that may be affecting your blood glucose without first discussing this with your GP.

When to Speak to Your GP About Your HbA1c Level

Anyone with an HbA1c of 6.0% should discuss the result with their GP, particularly if experiencing increased thirst, frequent urination, fatigue, blurred vision, or unintentional weight loss, which may indicate more significant glucose elevation.

Not sure if this is normal? Chat with one of our pharmacists →

If you have received an HbA1c result of 6.0% — whether flagged as abnormal or sitting at the lower boundary of the NDH range — it is advisable to discuss this with your GP or practice nurse, even if you feel well. Non-diabetic hyperglycaemia is often entirely asymptomatic, which is precisely why routine blood testing is so valuable. Early identification and intervention offer the best opportunity to prevent progression to type 2 diabetes.

You should seek a prompt GP appointment if you experience any of the following symptoms alongside a borderline HbA1c result:

• Increased thirst or frequent urination, particularly at night

• Unexplained fatigue or low energy

• Blurred vision

• Slow-healing wounds or recurrent infections

• Unintentional weight loss

These symptoms may suggest that blood glucose is rising more significantly than the HbA1c alone indicates, and further assessment would be warranted. In symptomatic individuals, a single HbA1c of 48 mmol/mol or above is sufficient to diagnose type 2 diabetes without the need for a confirmatory repeat test.

Urgent same-day assessment: If you or someone you know experiences rapid or significant unintentional weight loss, excessive thirst, frequent urination, vomiting, abdominal pain, or feels acutely unwell, seek same-day medical assessment — contact your GP urgently or call NHS 111. These symptoms may indicate type 1 diabetes or diabetic ketoacidosis (DKA), which requires prompt evaluation. In suspected type 1 diabetes, HbA1c alone should not be relied upon for diagnosis; capillary or plasma glucose and ketone measurements are needed, and urgent clinical assessment should be arranged without delay (NICE NG17).

For those without symptoms, a repeat HbA1c is typically recommended before any diagnosis of diabetes is confirmed. Your GP will also consider your overall cardiovascular risk, as elevated blood glucose frequently coexists with high blood pressure, raised cholesterol, and obesity — a cluster of risk factors known as metabolic syndrome. Addressing these collectively, rather than in isolation, is central to NICE-aligned preventive care.

Ultimately, an HbA1c of 6.0% is best viewed not as a cause for alarm, but as a timely and actionable signal. With appropriate support, many people successfully return their HbA1c to the low-risk range and significantly reduce their long-term health risks.

Frequently Asked Questions