Beda HbA1c NGSP dan IFCC adalah pertanyaan penting bagi klinisi, tenaga laboratorium, dan pasien yang menjumpai hasil HbA1c dalam satuan berbeda. HbA1c, atau haemoglobin terglikasi, merupakan pemeriksaan darah utama untuk memantau kontrol glukosa jangka panjang pada diabetes. Sistem NGSP melaporkan hasil dalam persentase (%), sedangkan sistem IFCC menggunakan satuan millimol per mol (mmol/mol). Memahami perbedaan keduanya sangat krusial untuk menghindari kesalahan interpretasi, terutama saat membandingkan hasil dari berbagai negara atau rekam medis lama.

Understanding HbA1c Measurement: NGSP and IFCC Explained

NGSP melaporkan HbA1c sebagai persentase dikalibrasi terhadap referensi DCCT, sedangkan IFCC menggunakan mmol/mol dengan prosedur referensi yang lebih spesifik secara analitik dan tertelusur ke material referensi internasional.

HbA1c, or glycated haemoglobin, is a key blood test used to assess long-term blood glucose control in people with diabetes or at risk of developing the condition. It reflects the average blood glucose level over the preceding two to three months, making it an invaluable tool for both diagnosis and ongoing monitoring.

Historically, HbA1c was measured and reported using the National Glycohemoglobin Standardization Program (NGSP) system, which expresses results as a percentage (%) . The NGSP is a standardisation network — not a single assay method — that aligns laboratory methods to the reference used in landmark US diabetes trials, principally the Diabetes Control and Complications Trial (DCCT). Because these trials used NGSP-aligned percentage values, this system became widely adopted internationally.

In response to growing concerns about inconsistency between laboratories worldwide, the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) developed a more precise, reference-based method. The IFCC system expresses HbA1c in millimoles per mole (mmol/mol), providing a standardised, SI-unit measurement traceable to a defined international reference material. This method measures only the specific fraction of haemoglobin glycated at the N-terminal valine of the beta chain, offering greater analytical specificity.

Both systems measure the same underlying biological phenomenon — the proportion of haemoglobin bound to glucose — but use different mathematical frameworks and reference standards. Understanding the distinction between NGSP and IFCC is essential for clinicians, laboratory professionals, and patients who may encounter results reported in either unit, particularly when reviewing historical records or international medical documentation.

Important: when HbA1c should not be used for diagnosis

HbA1c is not appropriate for diagnosing diabetes in all circumstances. Alternative tests — such as fasting plasma glucose, an oral glucose tolerance test (OGTT), or fructosamine — should be used in the following situations:

• Pregnancy (including suspected gestational diabetes — use OGTT per NICE NG3)

• Suspected type 1 diabetes (diagnosis should not rely on HbA1c alone; see NICE NG17 and NG18)

• Children and young people (HbA1c may not be appropriate; see NICE NG18)

• Acute illness, which can transiently alter results

• Recent blood transfusion or conditions causing rapid red cell turnover (e.g., haemolytic anaemia)

• Haemoglobin variants (e.g., sickle cell trait, HbC, HbE) that may interfere with certain assay methods

• Iron deficiency anaemia or other conditions altering red cell lifespan

• Chronic kidney disease with significantly altered red cell survival

In these situations, clinicians should discuss appropriate alternative diagnostic approaches with the patient.

Key Differences Between NGSP and IFCC HbA1c Units

Perbedaan utama adalah satuan: NGSP menggunakan % dan IFCC menggunakan mmol/mol, dengan nilai IFCC secara numerik lebih rendah — misalnya, 6,5% NGSP setara dengan 48 mmol/mol IFCC.

The most immediately apparent difference between the two systems is the unit of measurement:

• NGSP reports HbA1c as a percentage (%), e.g., 7.0%

• IFCC reports HbA1c in millimoles per mole (mmol/mol), e.g., 53 mmol/mol

Beyond the units themselves, the two systems differ in their reference measurement procedures. The NGSP method is calibrated against the DCCT reference, which measured total glycated haemoglobin relative to total haemoglobin. The IFCC method uses a highly specific reference procedure that isolates and quantifies only the glycated N-terminal valine of the haemoglobin beta chain, making it analytically more precise.

Because of these methodological differences, IFCC values are numerically lower than their NGSP equivalents for the same blood sample. For example, an NGSP value of 6.5% corresponds approximately to an IFCC value of 48 mmol/mol. This numerical discrepancy can cause confusion if clinicians or patients are unfamiliar with which system is being used.

The relationship between NGSP and IFCC values is linear across the routine clinical range, as defined by the internationally agreed NGSP–IFCC master equation (see the conversion section below). Small differences in results between laboratories may arise from method-specific or instrument-related biases and from rounding, but these do not reflect a fundamental non-linearity in the conversion itself.

During the UK transition period (approximately 2009–2011), many laboratories reported both units simultaneously to support clinical familiarity. UK NHS laboratories now report HbA1c exclusively in mmol/mol as standard; some may optionally display the NGSP percentage alongside, but this is not universal. Awareness of these differences remains particularly important when comparing results from different countries or reviewing older clinical records that predate the UK's adoption of IFCC reporting.

How the NHS and NICE Report HbA1c Results in the UK

NHS melaporkan HbA1c secara eksklusif dalam mmol/mol sejak 2011; NICE menetapkan 48 mmol/mol sebagai ambang diagnosis diabetes tipe 2 dan 42–47 mmol/mol sebagai non-diabetic hyperglycaemia (NDH).

The United Kingdom began transitioning HbA1c reporting in 2009, when NHS laboratories started moving from the NGSP percentage system to the IFCC mmol/mol system. This change was coordinated by the UK National External Quality Assessment Service (UK NEQAS) and the Association for Clinical Biochemistry and Laboratory Medicine (ACB), with support from professional bodies including Diabetes UK and the Joint British Diabetes Societies (JBDS). A period of dual reporting (displaying both mmol/mol and %) ran from approximately 2009 to 2011, after which mmol/mol became the exclusive standard across NHS laboratories in England, Scotland, Wales, and Northern Ireland.

This means that when a patient receives an HbA1c result from their GP surgery, hospital, or diabetes clinic, the value will be expressed in mmol/mol.

NICE guidelines reflect this reporting standard throughout their clinical guidance documents:

• NICE NG28 (Type 2 diabetes in adults) uses mmol/mol thresholds for diagnosis and treatment targets

• NICE NG17 (Type 1 diabetes in adults) similarly references IFCC values

• NICE NG18 (Diabetes in children and young people) provides guidance on when HbA1c may and may not be used

• NICE NG3 (Diabetes in pregnancy) specifies that HbA1c should not be used to diagnose gestational diabetes; OGTT-based criteria apply

• The NHS Diabetes Prevention Programme and NHS Health Check pathway also use mmol/mol

For diagnostic purposes, NICE and the NHS define a HbA1c of 48 mmol/mol or above as indicative of type 2 diabetes (confirmed on repeat testing in asymptomatic individuals), and a value of 42–47 mmol/mol as indicating non-diabetic hyperglycaemia (NDH) — the UK-preferred term for this intermediate range. The term 'prediabetes' is widely used in common parlance but is not the preferred clinical term in UK guidance. Clinicians trained internationally or reviewing older literature should be mindful that historical NGSP percentage values will need to be converted when applying current UK clinical thresholds.

Converting Between NGSP (%) and IFCC (mmol/mol) Values

Konversi menggunakan persamaan master: IFCC (mmol/mol) = [10,93 × NGSP (%)] − 23,50, atau NGSP (%) = [0,0915 × IFCC (mmol/mol)] + 2,15.

Converting between NGSP and IFCC values is straightforward using the IFCC–NGSP master equation, established through an international collaboration between the NGSP and IFCC networks and validated across the routine clinical range. The two primary conversion formulae are:

• IFCC to NGSP: NGSP (%) = [0.0915 × IFCC (mmol/mol)] + 2.15

• NGSP to IFCC: IFCC (mmol/mol) = [10.93 × NGSP (%)] − 23.50

For practical clinical use, a simplified approximation is often applied:

• Subtract approximately 2 from the NGSP percentage, then multiply by 10.93 to obtain the IFCC value

• Alternatively, divide the IFCC value by 10.93 and add 2.15 to obtain the NGSP percentage

Some commonly referenced conversion points include:

| NGSP (%) | IFCC (mmol/mol) | |---|---| | 5.0% | 31 | | 6.0% | 42 | | 6.5% | 48 | | 7.0% | 53 | | 8.0% | 64 | | 9.0% | 75 |

Please note that small differences may arise from rounding and from method- or instrument-specific laboratory biases. Where a laboratory-issued conversion is available, this should be preferred over manual calculation. Authoritative online conversion calculators are available via the NGSP website and from NHS and Diabetes UK resources.

Patients who have previously been managed in countries using NGSP reporting — such as the United States, Malaysia, or Indonesia — may present to UK clinicians with historical results expressed as percentages. In such cases, conversion is essential to ensure that treatment targets and diagnostic thresholds are applied correctly within the NHS framework. Patients are encouraged to ask their GP or diabetes nurse if they are uncertain which unit system their results are reported in.

Why Standardised HbA1c Reporting Matters for Diabetes Care

Pelaporan HbA1c yang terstandarisasi mencegah kesalahan diagnosis dan keputusan pengobatan yang tidak tepat akibat kebingungan satuan, serta memungkinkan perbandingan data klinis secara internasional.

Standardisation of HbA1c reporting is not merely a technical or administrative concern — it has direct implications for patient safety and clinical outcomes. When results are reported inconsistently or misinterpreted due to unit confusion, there is a risk of incorrect diagnosis, inappropriate treatment decisions, or failure to identify individuals at risk of diabetes complications.

The global adoption of IFCC reporting has been driven by the need for international comparability. As clinical trials, research publications, and patient populations increasingly cross national boundaries, having a single, analytically robust reference system allows clinicians and researchers to compare data with confidence. The IFCC method's traceability to a defined international reference material means that a result of 53 mmol/mol in a UK laboratory should be directly comparable to the same value measured in a laboratory in Germany, Australia, or Japan.

From a patient safety perspective, the transition to IFCC reporting in the UK required significant effort to educate both healthcare professionals and patients. During the transition period, UK safety bodies — including the National Patient Safety Agency (NPSA), UK NEQAS, and the ACB — issued guidance and alerts to prevent misinterpretation of results. Misreading an NGSP percentage as an IFCC value — or vice versa — could lead to:

• Undertreatment of poorly controlled diabetes if a high IFCC value is mistakenly interpreted as a lower NGSP percentage

• Unnecessary treatment escalation if a normal IFCC value is misread as an elevated NGSP percentage

• Diagnostic errors at the critical thresholds for non-diabetic hyperglycaemia (NDH) and diabetes

Ongoing professional education and patient-facing resources remain essential components of safe diabetes management in a globally connected healthcare environment.

Interpreting Your HbA1c Result: What the Numbers Mean

Di Inggris, HbA1c di bawah 42 mmol/mol dianggap normal, 42–47 mmol/mol menunjukkan NDH, dan 48 mmol/mol ke atas bersifat diagnostik untuk diabetes tipe 2 jika dikonfirmasi pada pemeriksaan ulang.

Understanding what your HbA1c result means in practical terms can help you engage more effectively with your diabetes care team. In the UK, results are reported in mmol/mol, and the following thresholds — aligned with NICE and NHS guidance — provide a useful framework for interpretation:

• Below 42 mmol/mol (approx. 6.0%): Normal range — no evidence of diabetes or non-diabetic hyperglycaemia

• 42–47 mmol/mol (approx. 6.0–6.4%): Non-diabetic hyperglycaemia (NDH) — indicates an increased risk of developing type 2 diabetes; lifestyle intervention is recommended. (This range is sometimes referred to as 'prediabetes' in common usage, but 'non-diabetic hyperglycaemia' is the preferred UK clinical term.)

• 48 mmol/mol (approx. 6.5%) or above: Diagnostic of type 2 diabetes when confirmed on a repeat test in asymptomatic individuals (per NICE NG28 and WHO 2011 criteria)

For people already diagnosed with diabetes, treatment targets are individualised and should be agreed with your care team. In line with NICE NG28 and NG17:

• 48 mmol/mol (6.5%) is the general target for many people with type 2 diabetes managed with lifestyle measures or metformin alone, or with medicines that do not carry a significant risk of hypoglycaemia

• 53 mmol/mol (7.0%) may be an appropriate target for those taking medicines associated with a risk of hypoglycaemia (such as insulin or a sulfonylurea), or where tighter control cannot be safely achieved

• For people with type 1 diabetes, NICE NG17 recommends aiming for 48 mmol/mol where this can be achieved safely; targets are always individualised

When HbA1c may not give a reliable result

HbA1c results can be affected by certain conditions that alter red cell lifespan or haemoglobin structure, including haemoglobin variants (e.g., sickle cell trait), haemolytic anaemia, iron deficiency anaemia, recent blood transfusion, and chronic kidney disease. In these situations, HbA1c may not accurately reflect average blood glucose, and your clinician may use an alternative test such as fructosamine, fasting plasma glucose, or an OGTT. HbA1c should also not be used to diagnose gestational diabetes (NICE NG3) or in children and young people with suspected type 1 diabetes (NICE NG18).

If your HbA1c result falls in the non-diabetic hyperglycaemia range or above, contact your GP to discuss further assessment and management. Early intervention can significantly reduce the risk of progression to type 2 diabetes and its associated complications.

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