Blood test HbA1c IFCC aligned results are the standard way NHS laboratories in the UK report long-term blood glucose control, expressed in millimoles per mole (mmol/mol) since 2011. The HbA1c test measures the proportion of glycated haemoglobin in your red blood cells, reflecting average blood glucose over the preceding two to three months. It is central to diagnosing type 2 diabetes and monitoring glycaemic control in people living with diabetes. This article explains what IFCC alignment means, how the test is performed, how to interpret your results using UK reference ranges, and what steps to take next.

What Is an HbA1c Blood Test and Why IFCC Alignment Matters

The HbA1c test measures glycated haemoglobin to reflect average blood glucose over two to three months; IFCC alignment ensures results are standardised and comparable across UK laboratories and internationally.

The HbA1c blood test measures the proportion of haemoglobin in your red blood cells that has become glycated — that is, chemically bonded with glucose. Red blood cells have a physiological lifespan of approximately 120 days, and because glycation accumulates progressively over this period, the HbA1c result reflects your average blood glucose levels over the preceding two to three months. This makes it a far more informative marker than a single fasting glucose reading.

HbA1c is central to the diagnosis and ongoing management of type 2 diabetes, and to the monitoring of glycaemic control in type 1 diabetes. It is important to note, however, that HbA1c is not appropriate for diagnosis in all situations. It should not be used to diagnose diabetes in the following groups:

• Children and young people

• Pregnant women (including for gestational diabetes)

• People with suspected type 1 diabetes

• People presenting with acute hyperglycaemia

• People with haemoglobin variants, haemolytic anaemia, or other conditions affecting red blood cell turnover

In these circumstances, plasma glucose-based tests — such as a fasting plasma glucose or an oral glucose tolerance test (OGTT) — are used instead.

For many years, HbA1c results were reported using the DCCT/NGSP percentage system (e.g., 6.5%), which was familiar from older clinical literature. However, this system had limitations in terms of international standardisation and analytical precision. To address this, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) developed a more chemically specific reference measurement procedure, and the UK transitioned to IFCC-aligned units — expressed in millimoles per mole (mmol/mol) — in 2011, in line with WHO and NICE recommendations (NICE NG28).

IFCC alignment matters because it ensures that HbA1c results are directly comparable across different laboratories, hospitals, and countries. This standardisation underpins the diagnostic thresholds recommended by NICE and the WHO, and supports safer, more reliable clinical decision-making for millions of people living with or at risk of diabetes in the UK.

Understanding IFCC-Aligned HbA1c Units Used in the UK

NHS laboratories report HbA1c in mmol/mol; 48 mmol/mol equals approximately 6.5% (the diabetes diagnostic threshold) and the two unit systems cannot be compared directly without conversion.

Since 2011, NHS laboratories in the UK report HbA1c results in IFCC units — millimoles per mole (mmol/mol). Some laboratories also display the DCCT/NGSP percentage value in parentheses for reference, but the IFCC mmol/mol figure is the primary reported result. The two systems are not interchangeable without conversion, and comparing them directly can lead to confusion.

The IFCC method works by specifically measuring only the glycated beta-chain N-terminal valine of haemoglobin, using highly controlled reference standards. This chemical specificity makes it more precise than the older percentage-based approach. The result is expressed as the number of mmol of glycated haemoglobin per mol of total haemoglobin — hence the unit mmol/mol.

For reference, some commonly used conversion points include:

• 48 mmol/mol is equivalent to approximately 6.5% (the diagnostic threshold for diabetes)

• 42 mmol/mol is equivalent to approximately 6.0% (the upper boundary of the prediabetes range)

• 53 mmol/mol is equivalent to approximately 7.0% (a common treatment target for many people with type 2 diabetes)

If you have older results in percentage format, your GP or diabetes team can convert these using validated tools. Recognised conversion resources include the IFCC/NGSP converter and the Diabetes UK HbA1c information and conversion page. Understanding which unit system your result is reported in is an essential first step before interpreting what the number means for your health.

How the HbA1c Test Is Carried Out on the NHS

A venous blood sample is taken without fasting and analysed by an IFCC-traceable accredited laboratory; point-of-care devices should not be used for diagnosis without laboratory confirmation.

The HbA1c blood test is a straightforward procedure typically performed in a GP surgery, NHS outpatient clinic, or community phlebotomy service. A healthcare professional — usually a phlebotomist or practice nurse — draws a small sample of venous blood, most commonly from a vein in the crook of your arm. The sample is collected into a specific tube containing an anticoagulant (usually EDTA) to prevent clotting, and is then sent to an accredited NHS laboratory for analysis.

One of the practical advantages of the HbA1c test is that no fasting is required beforehand. Unlike fasting plasma glucose tests, you can eat and drink normally before your appointment, which makes it more convenient. The test can be requested as part of a routine health check, an NHS Health Check, a diabetes review, or in response to symptoms suggestive of hyperglycaemia such as increased thirst, frequent urination, or unexplained fatigue.

For diagnostic purposes, NICE (NG28) recommends that HbA1c is measured using a venous blood sample analysed by a laboratory method that is traceable to the IFCC reference standard and subject to external quality assurance (EQA), such as participation in UK NEQAS for HbA1c. This ensures results are reliable and comparable.

In some clinical settings, point-of-care (POCT) HbA1c analysers are used, which can provide results within minutes from a fingerprick or small venous sample. However, POCT devices should not routinely be used for diagnosis. If a POCT result raises clinical suspicion of diabetes, it should be confirmed with a laboratory venous sample. Any POCT device used in clinical practice should meet MHRA quality assurance requirements. Once a laboratory result is available, it is typically communicated to you by your GP practice via an online patient portal, letter, or telephone consultation.

Interpreting Your IFCC HbA1c Results and Target Ranges

Below 42 mmol/mol is normal, 42–47 mmol/mol indicates prediabetes, and 48 mmol/mol or above confirms diabetes; treatment targets are individualised by your diabetes care team.

Understanding your IFCC HbA1c result requires knowing the clinically established reference ranges used in the UK. NICE (NG28) and WHO guidance defines the following key thresholds:

• Below 42 mmol/mol: Within the normal range — no evidence of prediabetes or diabetes based on this test alone

• 42–47 mmol/mol: Indicates prediabetes (also called non-diabetic hyperglycaemia or impaired glucose regulation) — an important risk period where lifestyle intervention can prevent progression

• 48 mmol/mol or above: Diagnostic of type 2 diabetes when confirmed on a second occasion in the absence of symptoms (or on a single occasion if symptoms of hyperglycaemia are present)

HbA1c should not be used for diagnosis in certain groups — including children, pregnant women, people with suspected type 1 diabetes, those presenting with acute hyperglycaemia, and those with haemoglobin variants or conditions affecting red blood cell turnover. In these situations, fasting plasma glucose or an OGTT should be used instead.

For people already diagnosed with diabetes, HbA1c is used to monitor glycaemic control over time. NICE recommends an individualised target, but commonly cited goals include:

• 48 mmol/mol (6.5%) for people newly diagnosed with type 2 diabetes managed by lifestyle or metformin alone

• 53 mmol/mol (7.0%) for those on medications that carry a risk of hypoglycaemia, or where a more relaxed target is clinically appropriate

• For type 1 diabetes, NICE (NG17) recommends aiming for 48 mmol/mol if achievable without problematic hypoglycaemia

HbA1c targets should always be discussed with your diabetes care team and tailored to your individual circumstances, including age, comorbidities, and treatment regimen. Your clinician will consider the full clinical picture rather than treating the number in isolation.

Factors That Can Affect HbA1c Accuracy and Reliability

Haemolytic anaemia, iron deficiency, haemoglobin variants, pregnancy, and certain medicines can falsely alter HbA1c results, requiring alternative glucose-based tests in affected individuals.

Although the IFCC-aligned HbA1c test is highly standardised, several physiological and clinical factors can affect the accuracy of results, and clinicians must be aware of these when interpreting findings.

Conditions affecting red blood cell turnover are among the most significant confounders. Because HbA1c reflects glycation over the lifespan of red blood cells (approximately 120 days), anything that shortens or lengthens that lifespan will alter the result:

• Haemolytic anaemia, recent blood transfusion, or significant blood loss can falsely lower HbA1c by reducing the proportion of older, more glycated cells

• Iron deficiency anaemia or vitamin B12/folate deficiency can falsely raise HbA1c by prolonging red cell survival

• Advanced chronic kidney disease and erythropoietin (EPO) therapy can also lower HbA1c by shortening red cell survival

Haemoglobin variants such as HbS (sickle cell trait), HbC, or HbE can interfere with some HbA1c assay methods, potentially producing unreliable results. In individuals with known haemoglobin variants or conditions affecting red cell turnover, alternative tests — such as fasting plasma glucose or an OGTT — are recommended for diagnosis. Fructosamine measurement may be considered for ongoing monitoring in these circumstances, but it is not a diagnostic test for diabetes.

Pregnancy affects HbA1c reliability due to physiological changes in red cell turnover. HbA1c should not be used to diagnose gestational diabetes. In the UK, NICE (NG3) recommends a 75 g oral glucose tolerance test (OGTT) at 24–28 weeks of pregnancy for women with identified risk factors.

Assay interferences: Certain medicines and supplements — including high-dose vitamin C and vitamin E — may interfere with some HbA1c assay methods. It is advisable to inform your GP of all medications and supplements you are taking. If your clinical team suspects a result may be unreliable, they will arrange confirmatory or alternative testing.

Next Steps After Receiving Your HbA1c Test Results

A prediabetes result warrants referral to the NHS Diabetes Prevention Programme; a confirmed diabetes result triggers structured education, possible metformin initiation, and regular HbA1c monitoring every three to six months.

Receiving your HbA1c result is the beginning of a clinical conversation, not the end of one. Depending on your result, your GP or diabetes care team will recommend a clear pathway forward.

If your result is in the prediabetes range (42–47 mmol/mol), this is an important opportunity for preventive action. NICE guidance (PH38) recommends referral to an evidence-based structured lifestyle programme, such as the NHS Diabetes Prevention Programme (NHS DPP), which focuses on dietary changes, increased physical activity, and weight management. Evidence from the NHS DPP and international trials indicates that sustained lifestyle modification can substantially reduce the risk of progression to type 2 diabetes.

If your result is 48 mmol/mol or above and diabetes is confirmed, your GP will discuss a management plan that may include:

• Referral to a structured diabetes education programme such as DESMOND (for type 2) or DAFNE (for type 1)

• Initiation of medication, most commonly metformin as first-line therapy for type 2 diabetes, in line with NICE NG28

• Regular HbA1c monitoring — typically every 3 to 6 months until stable on an unchanged treatment regimen, then every 6 months thereafter (NICE NG28)

Urgent assessment: If type 1 diabetes is suspected — for example, in a younger person with rapid weight loss, ketosis, or markedly elevated blood glucose — same-day specialist assessment should be arranged (NICE NG17). If you or someone else develops symptoms that may indicate diabetic ketoacidosis (DKA) or a hyperosmolar hyperglycaemic state (HHS) — such as vomiting, abdominal pain, drowsiness, rapid or laboured breathing, or severe dehydration — seek urgent same-day medical care or call 999.

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You should also contact your GP promptly if you experience symptoms such as extreme thirst, blurred vision, unexplained weight loss, or frequent infections, as these may indicate poorly controlled blood glucose requiring review.

For those with already-diagnosed diabetes whose HbA1c has risen above their agreed target, a medication review or intensification of treatment may be warranted. Equally, a result that has improved significantly is a positive sign worth acknowledging and building upon. Regular HbA1c monitoring, combined with open communication with your healthcare team, remains one of the most effective tools for long-term diabetes management in the UK.

Frequently Asked Questions