What Is a Good Glucose Level? UK Ranges

Understanding what is a good glucose level is essential for monitoring your health and identifying early signs of diabetes or blood sugar imbalance. In the UK, blood glucose is measured in millimoles per litre (mmol/L), and healthy ranges differ depending on whether you are fasting, eating, or managing an existing condition. This article explains normal glucose ranges for healthy adults, how readings are interpreted, how targets change for people with diabetes, what causes blood sugar to rise or fall, and when to seek advice from a GP.

What is a good glucose level for a healthy adult in the UK?

A healthy fasting blood glucose for an adult without diabetes is 4.0 to 5.9 mmol/L, with a post-meal reading below 7.8 mmol/L considered normal, in line with Diabetes UK and NHS guidance.

For a healthy adult without diabetes in the UK, a good fasting blood glucose level is generally between 4.0 and 5.9 mmol/L, and a reading below 7.8 mmol/L two hours after eating is considered normal. These ranges are consistent with figures published by Diabetes UK and used as reference points in NHS clinical practice, though individual laboratory reference intervals can vary slightly by assay and setting. Blood glucose is measured in millimoles per litre (mmol/L) in the UK, which differs from the mg/dL unit used in the United States, so it is important to use the correct scale when interpreting any result.

Blood glucose naturally fluctuates throughout the day in response to meals, physical activity, stress and sleep. In a person without diabetes, the body regulates these fluctuations tightly through the hormones insulin and glucagon, keeping levels within a relatively narrow range. A single reading outside the normal range does not automatically indicate a problem, but consistently elevated or low readings warrant further investigation.

If you are monitoring your glucose at home using a finger-prick device or a continuous glucose monitor (CGM), it is worth discussing your results with a GP or practice nurse, who can interpret them in the context of your overall health. Home devices vary in accuracy and are not used to diagnose diabetes. A laboratory venous blood test, either plasma glucose or HbA1c, remains the standard for diagnosis, as set out in NICE and NHS guidance.

What do blood sugar readings actually mean?

Different thresholds classify glucose readings as normal, borderline or raised; a fasting plasma glucose of 7.0 mmol/L or above or an HbA1c of 48 mmol/mol or above indicates type 2 diabetes under NICE NG28.

Blood sugar readings reflect the concentration of glucose circulating in your bloodstream at a given moment, and different thresholds are used to classify normal, borderline and raised levels.

According to NHS and NICE guidance (NICE NG28), a fasting plasma glucose of 6.1 to 6.9 mmol/L suggests impaired fasting glucose. In UK prevention programmes, the term 'non-diabetic hyperglycaemia' is also used, which may be identified by a fasting plasma glucose of 5.5 to 6.9 mmol/L or an HbA1c of 42 to 47 mmol/mol; this broader category is used to identify people at higher risk of developing type 2 diabetes. A fasting plasma glucose of 7.0 mmol/L or above on two separate occasions is consistent with a diagnosis of type 2 diabetes, unless there are unequivocal symptoms of hyperglycaemia, in which case a single result may be sufficient.

Other diagnostic thresholds include a random plasma glucose of 11.1 mmol/L or above in the presence of classic symptoms of diabetes (such as thirst, frequent urination and fatigue), or a two-hour plasma glucose of 11.1 mmol/L or above during an oral glucose tolerance test (OGTT). Where results are borderline or symptoms are absent, a confirmatory test on a separate day is usually required.

Another commonly used measure is the HbA1c test, which reflects average blood glucose over the preceding two to three months by measuring the proportion of haemoglobin that has glucose attached to it. An HbA1c below 42 mmol/mol is considered normal, a result of 42 to 47 mmol/mol indicates a raised risk of diabetes, and 48 mmol/mol or above is the diagnostic threshold for type 2 diabetes, as defined by NICE NG28.

HbA1c is not reliable in all situations. It should not be used to diagnose diabetes in pregnancy, in people with certain haemoglobinopathies (such as sickle cell disease or thalassaemia), in conditions associated with altered red cell turnover (including haemolytic anaemia or recent blood transfusion), or in children. In these circumstances, plasma glucose testing is used instead.

It is also helpful to understand the difference between:

• Fasting glucose: measured after at least eight hours without food or drink (other than water)

• Postprandial glucose: measured one to two hours after a meal

• Random glucose: taken at any time, regardless of when you last ate

• HbA1c: a longer-term average, not affected by what you ate that morning

Each test serves a different purpose, and your GP will choose the most appropriate one based on your symptoms and clinical history.

How do glucose targets differ for people with diabetes?

People with diabetes have personalised HbA1c targets, typically 48 mmol/mol for type 2 diabetes managed without hypoglycaemia risk or 53 mmol/mol when using insulin or sulphonylureas, as recommended by NICE NG28.

People living with diabetes have individualised glucose targets that are agreed with their healthcare team, and these differ from the reference ranges used for healthy adults.

NICE guideline NG28 recommends that adults with type 2 diabetes who are managed with lifestyle changes or certain medications aim for an HbA1c of 48 mmol/mol (6.5%), while those on medications that carry a risk of hypoglycaemia, such as sulphonylureas or insulin, may have a target of 53 mmol/mol (7.0%) to reduce the risk of low blood sugar episodes.

For people with type 1 diabetes, NICE guideline NG17 recommends an HbA1c target of 48 mmol/mol (6.5%) where this can be achieved safely, though individual targets may be higher depending on factors such as hypoglycaemia awareness, age and comorbidities. Self-monitoring of blood glucose is a central part of type 1 diabetes management, and many people use continuous glucose monitors (CGMs) to track their levels in real time.

Some newer medicines used in type 2 diabetes and weight management, such as GLP-1 receptor agonists, work partly by reducing postprandial glucose spikes and supporting weight loss, which in turn improves insulin sensitivity. These medicines are MHRA-authorised and NICE-recommended for specific patient groups, and decisions about their use are made by a prescriber following a clinical assessment. Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online weight-management consultations, with prescriber review and pharmacist support, where clinically appropriate options may be considered.

Pregnancy also changes glucose targets significantly. Women with gestational diabetes or pre-existing diabetes who are pregnant should follow the specific targets set out in NICE guideline NG3, which are tighter than standard adult targets. Your obstetric or diabetes team will provide personalised guidance on the fasting and post-meal thresholds to aim for during pregnancy.

What factors can cause your blood sugar to rise or fall?

Carbohydrate-rich meals, physical inactivity, stress, illness, certain medicines and poor sleep raise blood glucose, while skipping meals, intense exercise, excess insulin and alcohol can cause it to fall.

Blood sugar levels are influenced by a wide range of factors beyond diet alone, and understanding these can help you interpret your readings more accurately. The most common causes of a rise in blood glucose include:

• Carbohydrate-rich meals, particularly those high in refined sugars or white starch

• Physical inactivity, which reduces the muscles' ability to take up glucose

• Stress and illness, including acute infection and fever, which trigger the release of cortisol and adrenaline, both of which raise blood glucose

• Hormonal fluctuations, such as those associated with the menstrual cycle, which can affect insulin sensitivity

• Certain medicines, including corticosteroids, some antipsychotics and thiazide diuretics, which are recognised causes of raised blood glucose (as noted in NHS and BNF guidance)^[10]

• Poor sleep, which is associated with reduced insulin sensitivity

Conversely, blood glucose can fall (hypoglycaemia) due to:

• Skipping meals or prolonged fasting

• Intense or prolonged exercise

• Excess insulin or certain diabetes medicines such as sulphonylureas

• Alcohol consumption, particularly on an empty stomach, which impairs the liver's ability to release stored glucose; this risk can be delayed and may persist overnight

For people without diabetes, the body usually corrects mild dips in blood sugar quickly and without symptoms. However, in people taking glucose-lowering medicines, hypoglycaemia can become clinically significant. Symptoms include shakiness, sweating, confusion, palpitations and, in severe cases, loss of consciousness.

Lifestyle factors such as regular physical activity, a balanced diet rich in fibre and whole grains, adequate sleep and stress management all contribute to stable blood glucose levels. These are the foundations of both prevention and management of impaired glucose regulation, as outlined in NICE guideline PH38 on preventing type 2 diabetes.

When should you speak to a GP about your glucose levels?

Speak to a GP if your fasting glucose is 6.1 mmol/L or above, your HbA1c is 42 mmol/mol or above, or you have symptoms such as unexplained thirst, frequent urination or persistent fatigue.

You should speak to a GP if you have a fasting blood glucose reading of 6.1 mmol/L or above, an HbA1c of 42 mmol/mol or above, or if you experience symptoms that may suggest abnormal blood sugar. Symptoms that warrant a GP appointment include unexplained thirst, frequent urination, persistent fatigue, blurred vision, slow wound healing or unexplained weight loss, all of which can be associated with elevated blood glucose.

If you are using a home glucose monitor and record a reading of 11.1 mmol/L or above without a clear explanation, or if you experience repeated readings below 4.0 mmol/L, contact your GP for advice. A random plasma glucose of 11.1 mmol/L or above alongside classic symptoms of diabetes suggests the need for prompt same-week assessment and confirmatory testing. Home glucose meters are not used to diagnose diabetes; any result that concerns you should be followed up with a laboratory test.

In the event of a severe hypoglycaemic episode where someone is unconscious or unable to swallow, call 999 immediately, as this is a medical emergency. For urgent but non-emergency concerns about your glucose readings outside of GP hours, NHS 111 can provide advice.

Routine glucose screening is recommended by NICE (PH38) for adults at higher risk of type 2 diabetes, including those with a BMI above 25 kg/m2 (or above 23 kg/m2 in people of South Asian, Chinese, African-Caribbean or Black African descent), a family history of type 2 diabetes, or a history of gestational diabetes. Validated risk tools such as QDiabetes are used in primary care to identify people who would benefit from further assessment. If you fall into one of these groups and have not had a recent blood glucose check, it is worth raising this at your next GP appointment.

Suspected adverse reactions to any medicine affecting glucose levels can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Scientific References

1. High blood sugar (hyperglycaemia).
2. Type 2 diabetes in adults: management (NG28) – Blood glucose management chapter.
3. Type 2 diabetes: prevention in people at high risk (PH38) – Recommendations.
4. Type 2 diabetes: prevention in people at high risk (PH38).
5. Type 1 diabetes in adults: diagnosis and management (NG17) – Recommendations.
6. Type 1 diabetes | Treatment summaries – BNF – NICE.
7. Diabetes in pregnancy: management from preconception to the postnatal period (NG3) – Recommendations.
8. Diabetes in pregnancy: management from preconception to the postnatal period (NG3).
9. Hypoglycaemia | Treatment summaries – BNF – NICE.
10. Type 2 diabetes | Treatment summaries – BNF – NICE.
11. Low blood sugar (hypoglycaemia).
12. The threshold for diagnosing impaired fasting glucose.
13. Development and validation of QDiabetes-2018 risk prediction algorithm to estimate future risk of type 2 diabetes: cohort study. BMJ..
14. Different type 2 diabetes risk assessments predict dissimilar numbers at 'high risk': a retrospective analysis of diabetes risk-assessment tools. Br J Gen Pract..
15. The performance of seven QPrediction risk scores in an independent external sample of patients from general practice: a validation study. BMJ Open..

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