A blood sugar HbA1c test report can feel confusing at first glance, but understanding what the numbers mean is essential for managing your health. The HbA1c test measures your average blood glucose levels over the preceding two to three months, offering a far more comprehensive picture than a single finger-prick reading. Used routinely across the NHS for diagnosing and monitoring diabetes, the results are reported in mmol/mol and interpreted against clear NICE thresholds. This guide explains how to read your report, what the figures mean, which factors can affect accuracy, and what your next steps should be.

What Is an HbA1c Test and Why Is It Used in the UK?

The HbA1c test measures average blood glucose over 8–12 weeks by assessing glycated haemoglobin; it is the NHS's preferred diagnostic and monitoring tool for diabetes in adults, used in line with NICE NG28.

The HbA1c test — formally known as the glycated haemoglobin test — is a blood test used to measure your average blood sugar (glucose) levels over the preceding two to three months. Unlike a standard finger-prick glucose test, which only captures a single moment in time, the HbA1c provides a broader picture of how well blood sugar has been controlled over a sustained period. This makes it a particularly valuable tool in both diagnosing and monitoring diabetes.

In the UK, the HbA1c test is routinely used by GPs and specialist diabetes teams in line with guidance from the National Institute for Health and Care Excellence (NICE) and NHS England (NICE NG28). It is the preferred diagnostic test for Type 2 diabetes in most adults and is also used to monitor glycaemic control in people already living with Type 1 or Type 2 diabetes. For diagnostic purposes, the test must be carried out using a laboratory IFCC-standardised assay — typically via a venous blood sample taken at a GP surgery or clinic. Point-of-care (POC) devices that analyse a finger-prick sample are used in some settings, but these are generally reserved for monitoring only, where robust quality assurance is in place, and are not recommended for making a new diagnosis of diabetes.

The science behind the test lies in the behaviour of haemoglobin — the protein in red blood cells that carries oxygen. When glucose circulates in the bloodstream, it gradually attaches to haemoglobin in a process called glycation. Because red blood cells live for approximately 120 days, the proportion of glycated haemoglobin (HbA1c) reflects average blood glucose exposure over roughly the preceding 8–12 weeks, with more recent weeks contributing proportionally more to the result. A higher HbA1c indicates prolonged elevated blood sugar, which is associated with an increased risk of diabetes-related complications such as retinopathy, nephropathy, and cardiovascular disease.

When HbA1c should not be used to diagnose diabetes

HbA1c is not appropriate as a diagnostic test in all situations. It should not be used to diagnose diabetes in the following circumstances (WHO 2011; NICE NG28):

• Pregnancy or suspected gestational diabetes — an oral glucose tolerance test (OGTT) is used instead

• Suspected Type 1 diabetes or rapid-onset hyperglycaemia — clinical presentation and additional tests (e.g., C-peptide, islet autoantibodies) are required

• Children and young people — alternative diagnostic criteria apply

• Conditions affecting red blood cell turnover or haemoglobin structure — including haemolytic anaemia, haemoglobin variants (e.g., sickle cell trait, HbS, HbC), recent blood transfusion, or erythropoietin therapy

In these situations, fasting plasma glucose or an OGTT is preferred. Your GP or diabetes team will advise on the most appropriate test for your circumstances.

How to Read Your HbA1c Test Report Results

UK HbA1c results are reported in mmol/mol using the IFCC standard; your report will show your value, a reference range, and the test date, and should be interpreted by a clinician alongside your full medical history.

When you receive your HbA1c test report — whether through the NHS App, a patient portal, or a printed letter — the result is typically expressed in millimoles per mole (mmol/mol). This is the standardised unit used across the UK and Europe following the adoption of the IFCC (International Federation of Clinical Chemistry) reporting standard. You may occasionally see an older percentage figure (%) alongside it, particularly on historical reports or some private laboratory results, but mmol/mol is now the primary format used by NHS laboratories.

Your report will usually display:

• Your HbA1c value (e.g., 48 mmol/mol)

• A reference range or flagging system indicating whether the result is within normal limits, borderline, or elevated

• The date of the test and the requesting clinician's details

For diagnostic purposes, results should always be obtained using a quality-assured laboratory IFCC-standard method. If you have had a test through a private provider or a point-of-care device, your GP may request a confirmatory laboratory sample before making any clinical decisions.

In some cases, the laboratory may flag an HbA1c result as unreliable — for example, if you have a haemoglobin variant, significant anaemia, or another condition affecting red blood cell turnover. In these circumstances, your clinician may use alternative tests such as fasting plasma glucose, an OGTT, or markers such as fructosamine or glycated albumin.

It is important not to interpret your result in isolation. A single number on a report does not tell the full clinical story. For example, a result that appears slightly elevated may be influenced by recent illness, anaemia, or other factors (discussed in a later section). Equally, a result within the normal range does not automatically rule out all metabolic concerns if other symptoms are present.

If your result has been flagged as abnormal or you are unsure what it means, do not attempt to self-diagnose based on online calculators alone. Your GP or diabetes care team is best placed to contextualise the result alongside your medical history, symptoms, and any other investigations. Many NHS GP practices now include brief explanatory notes with results sent via online platforms, which can help guide your initial understanding before a formal consultation.

What HbA1c Levels Mean According to NHS and NICE Guidelines

Below 42 mmol/mol is normal, 42–47 mmol/mol indicates non-diabetic hyperglycaemia, and 48 mmol/mol or above is diagnostic of Type 2 diabetes in adults, per NICE NG28.

NICE and NHS England have established clear thresholds for interpreting HbA1c results in adults (NICE NG28). These thresholds guide clinical decision-making around diagnosis and ongoing management:

• Below 42 mmol/mol (approx. 6.0%) — considered within the normal range; diabetes is unlikely in the absence of other risk factors or symptoms

• 42–47 mmol/mol (approx. 6.0–6.4%) — classified as non-diabetic hyperglycaemia (sometimes referred to as 'prediabetes'); this indicates an elevated risk of developing Type 2 diabetes and warrants lifestyle intervention and regular monitoring

• 48 mmol/mol or above (approx. 6.5%) — in the appropriate clinical context, this is diagnostic of Type 2 diabetes, provided the result is confirmed on a second occasion (unless the person is symptomatic, in which case a single result may suffice)

For people already diagnosed with diabetes, NICE recommends individualised HbA1c targets rather than a one-size-fits-all approach:

• A target of 48 mmol/mol is recommended for most adults with Type 2 diabetes managed with lifestyle measures and/or medicines not associated with a risk of hypoglycaemia (such as metformin)

• A slightly higher target of 53 mmol/mol may be appropriate for those taking medicines that carry a risk of hypoglycaemia (such as sulfonylureas or insulin), to reduce the risk of low blood sugar episodes

In addition, NICE recommends early consideration of SGLT2 inhibitors (such as empagliflozin, dapagliflozin, or canagliflozin) for people with Type 2 diabetes who have established cardiovascular disease, heart failure, or chronic kidney disease, often alongside metformin. This reflects updated guidance in NICE NG28 and associated technology appraisals, and your GP or diabetes team will advise whether this applies to you.

In Type 1 diabetes, NICE guidance (NG17) recommends aiming for an HbA1c of 48 mmol/mol or below where this can be achieved safely without problematic hypoglycaemia.

It is worth noting that targets for children, older adults, pregnant women, and those with significant comorbidities may differ, and should always be agreed upon with a healthcare professional. The HbA1c is reviewed at least annually in people with diabetes, and more frequently (typically every three to six months) when treatment is being adjusted.

Factors That Can Affect Your HbA1c Reading

Haemolytic anaemia, haemoglobin variants, iron deficiency, recent blood transfusion, and EPO therapy can all cause falsely low or high HbA1c results, making alternative tests necessary in these situations.

While the HbA1c test is highly reliable, several physiological and clinical factors can influence the result, potentially leading to falsely high or falsely low readings. Being aware of these factors is important for accurate interpretation.

Conditions that may cause a falsely low HbA1c:

• Haemolytic anaemia — increased red blood cell turnover means cells are replaced more quickly, reducing the time available for glycation

• Iron deficiency anaemia (when treated with iron supplementation) — can lower HbA1c values

• Haemoglobin variants (e.g., sickle cell trait, HbS, HbC) — certain haemoglobin variants interfere with the assay used to measure HbA1c; in these cases, alternative tests such as fructosamine or glycated albumin may be used

• Recent blood transfusion — introduces new red blood cells, diluting the glycated fraction

• Erythropoietin (EPO) therapy — stimulates production of new red blood cells, which lowers the proportion of glycated haemoglobin

Conditions that may cause a falsely high HbA1c:

• Iron deficiency anaemia (untreated) — reduced red blood cell turnover can increase HbA1c

• Vitamin B12 or folate deficiency

• Splenectomy — prolongs red blood cell survival, increasing glycation time

Chronic kidney disease (CKD): CKD can make HbA1c results misleading in either direction. The effect depends on the degree of renal anaemia, whether erythropoietin-stimulating agents are being used, and the specific assay method employed. HbA1c should therefore be interpreted with particular caution in people with CKD, and alternative measures (such as fasting plasma glucose, OGTT, fructosamine, or glycated albumin) may be more appropriate.

Pregnancy: HbA1c is not recommended as a diagnostic tool during pregnancy due to physiological changes in red blood cell turnover. Gestational diabetes is diagnosed using an OGTT, in line with NICE guidance on diabetes in pregnancy.

When HbA1c is unreliable: If HbA1c cannot be reliably interpreted — due to haemoglobin variants, haemolysis, recent transfusion, EPO therapy, or significant anaemia — your clinician may use fasting plasma glucose, an OGTT, fructosamine, glycated albumin, or continuous glucose monitoring (CGM) or self-monitored blood glucose (SMBG) as alternatives.

There is no established link between short-term dietary changes immediately before the test and HbA1c results — unlike fasting glucose tests, the HbA1c is not affected by what you ate the day before. However, sustained dietary improvements over several weeks can genuinely lower the result. Always inform your GP or nurse of any relevant medical conditions or recent changes in health before your test.

Next Steps After Receiving Your HbA1c Results

Next steps depend on your result: normal readings require periodic monitoring if risk factors exist, non-diabetic hyperglycaemia prompts NHS DPP referral, and results of 48 mmol/mol or above lead to confirmatory testing and a diabetes management plan.

What happens after you receive your HbA1c result depends largely on where it falls and your individual clinical context. Understanding the likely pathway can help reduce anxiety and support informed decision-making.

If your result is in the normal range (below 42 mmol/mol): No immediate action is usually required. If you have risk factors for diabetes — such as obesity, a family history of Type 2 diabetes, or a history of gestational diabetes — your GP may recommend periodic retesting, typically every one to three years.

If your result indicates non-diabetic hyperglycaemia (42–47 mmol/mol): You are likely to be referred to or signposted towards the NHS Diabetes Prevention Programme (NHS DPP; 'Healthier You'), a nationally commissioned, evidence-based programme offering structured education, dietary advice, and physical activity support. NICE guidance recommends that people in this category are retested annually. Lifestyle changes — including a balanced diet, regular physical activity, and weight management — can meaningfully reduce HbA1c and lower the risk of progression to Type 2 diabetes.

If your result is 48 mmol/mol or above: Your GP will typically arrange a confirmatory repeat test (unless you are symptomatic) and discuss a management plan. This may include:

• Referral to a structured diabetes education programme such as DESMOND (for Type 2 diabetes)

• Initiation of medication — most commonly metformin as first-line pharmacotherapy per NICE NG28, with early consideration of an SGLT2 inhibitor for those with established cardiovascular disease, heart failure, or chronic kidney disease

• Dietary and lifestyle counselling

• Monitoring for complications through annual diabetes reviews

If you are prescribed a new medicine for diabetes, you can report any suspected side effects via the MHRA Yellow Card scheme at yellowcard.mhra.gov.uk. This is particularly relevant for medicines such as sulfonylureas or insulin, which can cause hypoglycaemia (low blood sugar).

When to contact your GP promptly: If you experience symptoms such as excessive thirst, frequent urination, unexplained weight loss, or blurred vision alongside an elevated result, seek a GP appointment without delay.

Urgent warning signs — seek emergency help immediately: If you or someone else develops symptoms that may suggest diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS) — including severe thirst, vomiting, abdominal pain, deep or laboured breathing, confusion, drowsiness, or signs of severe dehydration — call 999 or go to your nearest A&E immediately. If you are unsure whether symptoms are urgent, call NHS 111 for advice. Do not wait for a routine GP appointment in these circumstances.

Always keep a record of your HbA1c results over time — tracking trends is just as important as any single reading.

Key UK references: NICE NG28 (Type 2 diabetes in adults: management); NICE NG17 (Type 1 diabetes in adults); NHS HbA1c test information; WHO 2011 report on use of HbA1c for diabetes diagnosis; NHS Diabetes Prevention Programme (Healthier You); NICE guideline on diabetes in pregnancy; MHRA Yellow Card scheme.

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