Impaired fasting glucose (IFG) is a metabolic condition in which fasting blood glucose is elevated above normal but below the threshold for type 2 diabetes. In UK clinical practice, it is increasingly termed non-diabetic hyperglycaemia (NDH) and represents a critical window for intervention. Understanding the correct ICD-10 code for impaired fasting glucose is essential for accurate secondary care coding, population health surveillance, and referral pathways — including eligibility for the NHS Diabetes Prevention Programme. This article explains UK classification criteria, coding standards, risk factors, NICE-aligned management, and when to seek further assessment.

What Is Impaired Fasting Glucose and How Is It Classified?

IFG is defined by a fasting plasma glucose of 6.1–6.9 mmol/L (WHO criteria) and represents an intermediate state between normal glucose regulation and type 2 diabetes, known in NHS practice as non-diabetic hyperglycaemia (NDH).

Impaired fasting glucose (IFG) is a metabolic condition in which blood glucose levels are higher than normal after a period of fasting, but not high enough to meet the diagnostic threshold for type 2 diabetes. In UK clinical practice, it is increasingly referred to as non-diabetic hyperglycaemia (NDH) — the preferred NHS and Public Health England/UKHSA term — and represents an intermediate state between normal glucose regulation and overt diabetes mellitus.

In the United Kingdom, the World Health Organisation (WHO) 2006 criteria are used for the formal IFG classification. A fasting plasma glucose level of 6.1 to 6.9 mmol/L meets the WHO definition of IFG. However, for the purposes of NHS prevention programmes and risk stratification, the NDH band is broader: a fasting plasma glucose of 5.5–6.9 mmol/L is used to identify individuals eligible for the NHS Diabetes Prevention Programme (NHS DPP). A fasting glucose of 7.0 mmol/L or above on two separate occasions (or once if accompanied by symptoms of diabetes) is diagnostic of diabetes mellitus. Clinical context always determines which threshold is most relevant.

IFG reflects reduced insulin sensitivity and, in many cases, early impairment in the first-phase insulin secretory response from pancreatic beta cells. This means the body is less efficient at clearing glucose from the bloodstream following an overnight fast.

For completeness, impaired glucose tolerance (IGT) — a related condition identified via an oral glucose tolerance test (OGTT) — is defined by a 2-hour plasma glucose of 7.8–11.0 mmol/L (WHO criteria). IFG and IGT can coexist, and individuals with both carry a higher risk of progression to type 2 diabetes than those with either condition alone.

It is important to note that HbA1c is not appropriate for diagnosing IFG or NDH in all situations. HbA1c results may be unreliable in pregnancy, suspected type 1 diabetes, children and young people, haemoglobinopathies (e.g., sickle cell disease, thalassaemia), certain anaemias, chronic kidney disease, and following recent blood transfusion. In these circumstances, fasting plasma glucose or an OGTT should be used instead.

IFG does not cause symptoms in most people — it is typically identified incidentally through routine blood tests or targeted screening in individuals with known risk factors. Early identification is clinically significant because it allows timely lifestyle intervention, which evidence consistently shows can delay or prevent progression to type 2 diabetes.

ICD-10 Code for Impaired Fasting Glucose in UK Clinical Practice

In UK secondary care, IFG is coded under ICD-10 category R73 (Abnormal glucose regulation); primary care uses SNOMED CT, and the US-specific code R73.01 is not applicable in NHS settings.

It is important to understand that different coding systems are used in different parts of the NHS:

• Primary care (GP practices) in England is mandated to use SNOMED CT (Systematized Nomenclature of Medicine – Clinical Terms) for clinical record-keeping, including the recording of NDH/IFG. NHS England's information standards require SNOMED CT as the clinical terminology system in GP systems.

• Secondary care (hospitals, outpatient departments) uses ICD-10 for episode coding, clinical audit, and national data submissions such as Hospital Episode Statistics (HES).

For secondary care ICD-10 coding, impaired fasting glucose and related states of abnormal glucose regulation are classified under R73 — Abnormal glucose regulation. The specific assignment within this category should follow the NHS Digital National Clinical Coding Standards ICD-10 (5th Edition) and any associated Data Coding Standards (DCS). Clinicians and medical coders should consult their local clinical coding team to ensure accurate and consistent documentation, as the precise code applied will depend on the clinical information available in the record.

Note: The sub-code R73.01 is a US ICD-10-CM code and is not used in the UK. UK NHS coding is based on the WHO ICD-10 system, not the US Clinical Modification (ICD-10-CM). Any reference to R73.01 in a UK context is incorrect.

Proper coding for IFG/NDH has real implications for:

• Population health surveillance, enabling NHS bodies to track NDH prevalence

• Referral pathways, including eligibility for the NHS Diabetes Prevention Programme (NHS DPP)

• Research and audit, supporting evidence-based service planning

Healthcare professionals documenting IFG/NDH should ensure the diagnosis is clearly recorded in the patient's medical record alongside the fasting glucose value and the date of the test. This supports continuity of care and appropriate follow-up. If there is uncertainty about the correct code to apply, liaison with the clinical coding team within the trust or Integrated Care Board (ICB) is recommended.

Risk Factors and What Your Results Mean

IFG carries an approximately 5–10% annual risk of progression to type 2 diabetes; key risk factors include obesity, physical inactivity, family history, South Asian or Black African/Caribbean ethnicity, and gestational diabetes history.

Receiving a result that falls within the impaired fasting glucose or NDH range can feel concerning, but it is important to understand that IFG is not a diagnosis of diabetes. It is, however, a meaningful signal that warrants attention. Evidence from UK and international public health sources indicates that individuals with IFG have an approximately 5–10% annual risk of progressing to type 2 diabetes, though this risk can be substantially modified through lifestyle change.

Several well-established risk factors are associated with the development of IFG and progression to type 2 diabetes:

• Overweight or obesity, particularly central (abdominal) adiposity

• Physical inactivity and a sedentary lifestyle

• Family history of type 2 diabetes in a first-degree relative

• Ethnicity — South Asian, Black African, and Black Caribbean populations are at higher risk and may develop diabetes at a lower BMI

• Age — risk increases with advancing age, particularly over 40 years (over 25 years in South Asian populations)

• History of gestational diabetes or polycystic ovary syndrome (PCOS)

• Hypertension or dyslipidaemia (raised triglycerides or low HDL cholesterol)

• Use of certain medications, including corticosteroids and some antipsychotics

A fasting glucose result in the IFG range should always be interpreted alongside the full clinical picture. To confirm a diagnosis of diabetes, two abnormal results are generally required (using the same or different tests on separate occasions), unless the person is symptomatic with markedly elevated glucose. For classifying NDH, a repeat fasting plasma glucose or HbA1c measurement is appropriate, as recommended by NICE (NG28).

HbA1c levels of 42–47 mmol/mol (6.0–6.4%) are considered indicative of NDH/prediabetes in the UK context. However, HbA1c should not be used where results may be unreliable — for example, in pregnancy, haemoglobinopathies, certain anaemias, chronic kidney disease, or following recent blood transfusion. In these situations, fasting plasma glucose or an OGTT is preferred.

It is also worth noting that IFG and impaired glucose tolerance (IGT) — identified via an OGTT with a 2-hour plasma glucose of 7.8–11.0 mmol/L — can coexist, and individuals with both conditions carry a higher risk of progression than those with either condition alone.

NICE Guidelines on Managing Impaired Fasting Glucose

NICE recommends intensive lifestyle intervention — including at least 150 minutes of moderate activity weekly and a 5–7% weight reduction if overweight — plus referral to the NHS Diabetes Prevention Programme for eligible individuals.

NICE guidance provides a clear framework for managing individuals identified with NDH/IFG. The key documents are NICE PH38 (Type 2 diabetes: prevention in people at high risk), which addresses individual-level interventions, and NICE PH35 (Preventing type 2 diabetes: population and community-level interventions), which addresses broader public health approaches. The cornerstone of management is intensive lifestyle intervention, which has been shown in landmark trials — including the US Diabetes Prevention Programme (DPP) and the Finnish Diabetes Prevention Study — to reduce progression to type 2 diabetes by up to 58%.

Key NICE-aligned recommendations for individuals with IFG/NDH include:

Lifestyle modification:

• Achieving and maintaining a 5–7% reduction in body weight if overweight

• Engaging in at least 150 minutes of moderate-intensity physical activity per week

• Adopting a balanced, lower-calorie diet rich in fibre, vegetables, and wholegrains, with reduced saturated fat and refined carbohydrate intake

• Reducing alcohol consumption and stopping smoking where applicable

NHS Diabetes Prevention Programme (NHS DPP): Eligible individuals — those with an HbA1c of 42–47 mmol/mol or a fasting plasma glucose of 5.5–6.9 mmol/L (within the preceding 12 months, per NHS England service specification) — should be referred to the NHS DPP, a structured, evidence-based behaviour change programme delivered in group or digital formats.

Pharmacological intervention: There is currently no licensed medication in the UK specifically indicated for IFG or NDH. Metformin is not routinely recommended for prevention of type 2 diabetes in NICE guidance. However, NICE PH38 advises that metformin may be considered on an off-label basis for specific high-risk adults — for example, those whose blood glucose is rising despite intensive lifestyle intervention, those with a higher BMI, those aged under 60, or those with a history of gestational diabetes — following a careful discussion of risks and benefits, and with attention to contraindications (including renal impairment). Prescribers should refer to the BNF and the MHRA-approved Summary of Product Characteristics (SmPC) for metformin regarding licensed indications and safety.

Monitoring: NICE recommends that individuals with IFG/NDH have their HbA1c or fasting glucose reviewed at least annually to monitor for progression. Where HbA1c is unreliable (e.g., in pregnancy or haemoglobinopathies), plasma glucose measures should be used. Blood pressure, lipid profile, and renal function should also be assessed as part of cardiovascular risk management.

When to Seek Further Assessment from Your GP

Seek same-day urgent care if symptoms suggest DKA or new-onset type 1 diabetes; contact your GP promptly if fasting glucose reaches 7.0 mmol/L or above, symptoms of diabetes develop, or you are pregnant or planning pregnancy.

For most people, impaired fasting glucose is managed in primary care with lifestyle support and regular monitoring. However, there are specific circumstances in which it is important to seek further assessment from your GP or healthcare team.

Seek urgent same-day medical attention if you experience:

• Symptoms that may suggest diabetic ketoacidosis (DKA) — such as abdominal pain, vomiting, rapid or laboured breathing, or drowsiness — particularly if you have very high blood glucose. DKA is a medical emergency; call 999 or go to your nearest A&E.

• Symptoms that may suggest new-onset type 1 diabetes, including rapid onset of thirst, frequent urination, unexplained weight loss, and fatigue — especially in younger people. This requires same-day clinical assessment.

Contact your GP promptly if you notice:

• Symptoms suggestive of diabetes, including increased thirst, frequent urination (particularly at night), unexplained weight loss, fatigue, or blurred vision — these may indicate that blood glucose levels have risen into the diabetic range

• A fasting glucose result of 7.0 mmol/L or above, or an HbA1c of 48 mmol/mol or higher — note that a single result in the diabetic range generally requires confirmation with a repeat test (unless you have clear symptoms of diabetes with markedly elevated glucose), as recommended by NICE NG28

• Significant weight gain or a marked reduction in physical activity, which may accelerate progression

• Pregnancy or planning a pregnancy — women with IFG/NDH require closer monitoring during pregnancy due to the increased risk of gestational diabetes and associated complications; your care should be guided by NICE NG3 (Diabetes in pregnancy)

• Starting a new medication known to affect glucose metabolism, such as corticosteroids or certain antipsychotics

Even in the absence of symptoms, it is important not to miss your annual review appointment. Regular monitoring allows your GP to detect any deterioration early and adjust your management plan accordingly. If you have not been referred to the NHS Diabetes Prevention Programme and believe you may be eligible, ask your GP or practice nurse about this during your next appointment.

If you have concerns about your results or feel uncertain about what your IFG/NDH diagnosis means for your long-term health, do not hesitate to raise these with your GP. Understanding your risk is the first step towards taking meaningful action, and with the right support, many people with IFG successfully prevent or significantly delay the onset of type 2 diabetes.

Frequently Asked Questions