HbA1c and A1c refer to exactly the same blood test — a point of frequent confusion for people researching diabetes care across UK and US sources. HbA1c is the standard term used in the United Kingdom by the NHS, NICE, and clinical laboratories, whilst A1c is the shorthand preferred in the United States. Both measure glycated haemoglobin to reflect average blood glucose levels over the preceding 8 to 12 weeks. This article explains what the test measures, how UK results are reported, what your numbers mean, factors that can affect accuracy, and when to speak to your GP.

HbA1c and A1c: Are They the Same Test?

Yes, HbA1c and A1c are the same test — HbA1c is the UK standard term and A1c is used in the US; both measure the percentage of glycated haemoglobin to reflect average blood glucose over 8 to 12 weeks.

In short, yes — HbA1c and A1c refer to the same blood test. The term 'A1c' is predominantly used in the United States, whilst 'HbA1c' is the standard terminology used in the United Kingdom, preferred by the NHS, NICE, and UK clinical laboratories, which report results in IFCC units (mmol/mol). Both names describe an identical laboratory measurement, so if you have encountered both terms whilst researching your diabetes care, there is no need for concern — they are interchangeable.

The full name for the test is glycated haemoglobin, sometimes written as haemoglobin A1c. Haemoglobin is the protein found inside red blood cells that carries oxygen around the body. Red blood cells have a lifespan of approximately 120 days. As glucose circulates in the bloodstream, it gradually attaches to haemoglobin in a process called glycation. The HbA1c test measures the percentage of haemoglobin that has become glycated, providing a reliable picture of average blood glucose levels over roughly the preceding 8 to 12 weeks, with greater weighting given to more recent weeks.

This longer-term view makes HbA1c considerably more informative than a single fasting glucose reading, which only reflects blood sugar at one specific moment. Because of this, HbA1c is used both to diagnose type 2 diabetes and to monitor ongoing glucose control in people already living with type 1 or type 2 diabetes. NICE guidelines recommend HbA1c as the primary diagnostic tool for type 2 diabetes in most adults, with a result of 48 mmol/mol (6.5%) or above confirming a diagnosis. In people without symptoms, this should be confirmed on a second separate sample. However, if classic symptoms of hyperglycaemia are present (such as thirst, polyuria, or unexplained weight loss), a single diagnostic result may be sufficient, or plasma glucose criteria may be used instead. Please discuss your individual circumstances with your GP or diabetes care team.

Key UK references: NICE NG28 (Type 2 diabetes in adults: management); WHO 2011 — Use of glycated haemoglobin (HbA1c) in the diagnosis of diabetes mellitus; NHS: Type 2 diabetes — diagnosis.

Understanding Your HbA1c Results and Target Ranges

UK HbA1c results are reported in mmol/mol; 48 mmol/mol (6.5%) or above diagnoses type 2 diabetes, whilst 42–47 mmol/mol indicates prediabetes and individual treatment targets vary based on clinical circumstances.

HbA1c results in the UK are reported in mmol/mol, following the IFCC (International Federation of Clinical Chemistry) standardisation adopted in 2009. Older reports or international sources may still use the percentage (%) format (NGSP units), which can occasionally cause confusion. A quick reference for common values is helpful:

• Below 42 mmol/mol (6.0%) — Within the normal range for most adults; however, if you have symptoms or a condition that may affect HbA1c reliability, further clinical assessment and plasma glucose testing may still be warranted

• 42–47 mmol/mol (6.0–6.4%) — Prediabetes (non-diabetic hyperglycaemia); increased risk of developing type 2 diabetes

• 48 mmol/mol (6.5%) or above — Diagnostic threshold for type 2 diabetes

It is important to note that HbA1c is not used to diagnose gestational diabetes; different testing approaches (typically an oral glucose tolerance test) are used during pregnancy, and monitoring targets in pregnancy also differ.

For people already diagnosed with diabetes, NICE sets individualised HbA1c targets depending on treatment and personal circumstances. As a general guide:

• 48 mmol/mol (6.5%) is the target for most people with type 2 diabetes managed by lifestyle or metformin alone

• 53 mmol/mol (7.0%) is often the target for those on medications that carry a risk of hypoglycaemia, such as sulfonylureas or insulin

• For type 1 diabetes, NICE recommends aiming for 48 mmol/mol (6.5%) where safely achievable

HbA1c targets are not one-size-fits-all. Factors such as age, frailty, risk of hypoglycaemia, cardiovascular history, and personal preference all influence what constitutes an appropriate target for an individual. Your GP or diabetes care team will discuss a personalised target with you. Achieving a lower HbA1c is generally associated with a reduced risk of long-term diabetes complications, including retinopathy, nephropathy, and neuropathy, but overly aggressive glucose lowering can increase the risk of hypoglycaemia, particularly in older adults.

If you are taking a medication that may cause hypoglycaemia and you experience suspected side effects, you can report these to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

Key UK references: NICE NG28 (targets and monitoring); NICE NG17 (Type 1 diabetes in adults: diagnosis and management); NHS: HbA1c test.

Factors That Can Affect HbA1c Accuracy

Conditions including haemolytic anaemia, iron deficiency, haemoglobin variants, and chronic kidney disease can cause falsely low or high HbA1c results, making plasma glucose or OGTT preferable in these situations.

Whilst HbA1c is a robust and widely validated test, certain medical conditions and biological factors can affect its accuracy, potentially leading to falsely high or falsely low results. Clinicians are trained to interpret HbA1c in the context of a patient's full medical history, and it is important to be aware of these limitations.

Conditions that may cause a falsely low HbA1c include:

• Haemolytic anaemia (where red blood cells are destroyed more rapidly, reducing glycation time)

• Iron deficiency anaemia treated with iron supplementation

• Recent significant blood loss or blood transfusion

• Haemoglobin variants such as sickle cell trait or haemoglobin C disease

• Pregnancy, particularly in the second and third trimesters

Conditions that may cause a falsely high HbA1c include:

• Iron deficiency anaemia (before treatment)

• Vitamin B12 or folate deficiency

• Splenectomy (removal of the spleen), which prolongs red blood cell lifespan

• Chronic kidney disease (CKD); in advanced CKD (stages 4–5), dialysis, or where erythropoiesis-stimulating agents (ESAs) are used, HbA1c may be unreliable and should be interpreted with caution

Populations and situations in which HbA1c is not suitable for diagnosis include:

• Children and young people

• Suspected type 1 diabetes at any age

• Pregnancy (including suspected gestational diabetes)

• Acute illness

• Symptoms of diabetes present for fewer than two months (HbA1c may not yet reflect the degree of hyperglycaemia)

• Haemoglobin variants or haemolytic conditions

• Recent blood transfusion

In these situations, fasting plasma glucose or an oral glucose tolerance test (OGTT) should be used for diagnosis. For ongoing monitoring when HbA1c is unreliable, alternatives such as fructosamine, glycated albumin, or continuous glucose monitoring (CGM) may be considered.

Some medications can also interfere with HbA1c measurements. Hydroxyurea (used in sickle cell disease) and dapsone (which can cause haemolysis) are notable examples. Always inform your healthcare team of all medications you are taking so that results can be interpreted accurately.

Key UK references: NICE CKS — Type 2 diabetes (diagnosis); WHO 2011 — Use of HbA1c in the diagnosis of diabetes mellitus; RCPath/UK NEQAS guidance on HbA1c assay interferences.

When to Speak to Your GP About Your HbA1c Level

Contact your GP if your HbA1c is 42 mmol/mol or above, has risen significantly, or if you have symptoms of poorly controlled blood glucose such as increased thirst, frequent urination, or unexplained weight loss.

Knowing when to seek medical advice about your HbA1c result is an important part of managing your health proactively. Whether you have received a result through a routine NHS health check, a pharmacy screening service, or as part of ongoing diabetes monitoring, there are several situations in which you should contact your GP or diabetes care team.

Seek urgent same-day care (call 999, 111, or go to A&E) if you or someone with diabetes is:

• Severely unwell, vomiting, or has abdominal pain

• Drowsy, confused, or difficult to rouse

• Breathing rapidly or showing signs of dehydration

These may be signs of diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS), both of which require immediate medical attention.

Contact your GP if:

• Your HbA1c result is 42 mmol/mol or above and you have not previously been told you are at risk of diabetes

• Your HbA1c has risen significantly since your last test, even if it remains within your target range

• You are experiencing symptoms that may suggest poorly controlled blood glucose, such as increased thirst, frequent urination, unexplained weight loss, fatigue, or recurrent infections

• You are concerned that a medical condition or new medication may be affecting your result

• Your HbA1c is consistently below your agreed target, which may indicate a risk of hypoglycaemia, particularly if you are on insulin or a sulfonylurea

For people already living with diabetes, NICE recommends that HbA1c is checked every three to six months when treatment is being adjusted, and every six months once glucose control is stable. Missing routine monitoring appointments can mean that deteriorating glucose control goes undetected, increasing the risk of long-term complications.

If you are in the prediabetes range (42–47 mmol/mol), your GP may refer you to the Healthier You: NHS Diabetes Prevention Programme, a structured lifestyle intervention shown to significantly reduce the risk of progressing to type 2 diabetes. Early engagement with this programme, alongside dietary changes and increased physical activity, can be highly effective. Never ignore a borderline result — early action offers the best opportunity to protect your long-term health.

Key UK references: NICE NG28 (monitoring frequency); NHS: Type 2 diabetes — symptoms and urgent advice; Healthier You: NHS Diabetes Prevention Programme (NHS England).

Frequently Asked Questions