Prediabetes: catching blood sugar risk early in the UK

Prediabetes means blood glucose is higher than normal but not high enough for a diabetes diagnosis. In the UK it is often called non-diabetic hyperglycaemia, and the usual HbA1c range is 42 to 47 mmol/mol. It is not a failure or a guaranteed path to type 2 diabetes: it is an early warning that gives you time to improve weight, waist, food quality, activity, sleep, blood pressure and lipid risk before permanent diabetes care is needed.¹²

What prediabetes is

Prediabetes is a risk state, not a separate disease with a guaranteed outcome. It means your blood glucose control has drifted above the healthy range, usually because insulin resistance is rising or the pancreas is working harder to keep glucose normal. The label is useful only if it leads to action. It should not become a reason for shame, panic or extreme dieting.

Diabetes UK explains that prediabetes, sometimes called borderline diabetes, means blood sugar levels are higher than they should be, 42 to 47 mmol/mol on HbA1c, and there are not usually symptoms.² NHS type 2 diabetes guidance similarly says prediabetes means glucose is higher than normal but not high enough for diabetes, and that most people do not have symptoms such as peeing more, tiredness and unplanned weight loss.¹

The reason to catch it early is that type 2 diabetes usually develops gradually. Blood pressure, waist size, triglycerides, fatty liver, sleep apnoea, PCOS, medication effects, family history and ethnicity can all signal risk before symptoms appear. Prediabetes is the point where those signals can still be changed without assuming lifelong medication is inevitable.

The tests and UK thresholds

The common UK test is HbA1c. It estimates average blood glucose over the previous 2 to 3 months by measuring how much glucose has attached to haemoglobin in red blood cells. It does not require fasting, which makes it practical for GP and NHS Health Check use. Fasting plasma glucose is also used, and sometimes an oral glucose tolerance test is needed, especially when pregnancy, previous gestational diabetes or borderline results make the picture more complex.

NICE guidance for type 2 diabetes prevention says trained professionals should offer venous blood tests, fasting plasma glucose or HbA1c, to adults with high risk scores, and that fasting plasma glucose of 5.5 to 6.9 mmol/L or HbA1c of 42 to 47 mmol/mol indicates high risk.³

HbA1c is useful, but not perfect. It can be less reliable in some anaemias, recent blood loss, pregnancy, haemoglobin variants, chronic kidney disease and conditions affecting red blood cell turnover. If the number does not fit the story, ask whether fasting glucose, repeat HbA1c or an oral glucose tolerance test would be more appropriate.

Who should be checked early

NHS type 2 diabetes guidance says risk is higher if you are white and over 40, or over 25 and from a South Asian, Chinese, Black African or Black Caribbean ethnic background, if a parent or sibling has diabetes, if you are overweight and not very physically active, or if you have a condition that increases risk such as high blood pressure.¹

Other early clues include a waist that has increased over time, high triglycerides, low HDL cholesterol, fatty liver, PCOS, previous gestational diabetes, sleep apnoea, recurrent thrush, steroid use, antipsychotic medication, family history of early type 2 diabetes, and a history of large babies in pregnancy. None of these proves prediabetes, but they should lower the threshold for checking HbA1c and cardiovascular risk.

Symptoms matter too. NHS lists common type 2 diabetes symptoms as feeling very tired, peeing more than usual, feeling thirsty all the time and losing weight without trying, with possible blurred vision, slow-healing cuts and genital itching or recurrent thrush.¹ Prediabetes usually has no symptoms, so symptoms like these should not be parked as "just prediabetes". They need assessment for diabetes and other causes.

What actually lowers risk

The most proven intervention is not a supplement. It is a structured lifestyle programme that changes weight, food pattern and activity enough to reduce insulin resistance. The Diabetes Prevention Program Research Group randomised 3,234 high-risk adults to intensive lifestyle intervention, metformin or placebo. The lifestyle programme aimed for at least 7% weight loss and at least 150 minutes of physical activity per week, and reduced diabetes incidence by 58% compared with placebo over a mean 2.8 years.⁵

That does not mean everyone must lose exactly 7% before anything counts. It means modest, sustained weight reduction is biologically powerful when excess visceral fat is part of the risk. Waist reduction often matters more than chasing a perfect scale number. Muscle also matters because skeletal muscle is a major glucose sink, so walking, cycling, stairs, resistance training and breaking up long sitting all improve the signal.

Food quality should be practical. The strongest pattern for many people is: more protein at breakfast and lunch, more high-fibre foods, more vegetables and pulses if tolerated, fewer sugary drinks, fewer refined starches eaten alone, less alcohol if it drives snacking or triglycerides, and meals that keep you full for 4 to 5 hours. This is not about banning carbohydrates. It is about replacing fast, low-fibre, easy-to-overeat carbohydrates with meals that your body handles better.

Sleep and stress are not side issues. Short sleep, untreated sleep apnoea and chronic stress can raise appetite, reduce activity, worsen glucose control and make evening eating harder. If HbA1c is rising despite "good food", ask about snoring, daytime sleepiness, shift work, steroid medication, perimenopause, depression, pain and alcohol. The insulin resistance guide explains the wider pattern beyond a single glucose number.

Where the NHS programme fits

Healthier You, the NHS Diabetes Prevention Programme in England, is designed for people at high risk of type 2 diabetes. Current programme information says eligibility includes being 18 or older, not pregnant, and having high glucose levels, usually an HbA1c between 42 and 47.9 mmol/mol, fasting plasma glucose 5.5 to 6.9 mmol/L, or a history of gestational diabetes.⁴

Real-world evidence supports the programme, with modest average changes rather than miracle results. Valabhji and colleagues reported early outcomes from the English NHS Diabetes Prevention Programme using national service-level data, finding mean weight loss of about 3.3 kg and HbA1c reduction of about 2.04 mmol/mol among attendees with paired data.⁶ Average does not mean trivial. At population level, small sustained shifts can prevent many diagnoses.

Metformin can be part of diabetes prevention for selected higher-risk people, but it is not the first conversation for everyone in UK primary care. In the Diabetes Prevention Program, metformin reduced diabetes incidence by 31% compared with placebo, less than the lifestyle intervention overall.⁵ It may be more relevant where risk is higher, previous gestational diabetes is present, or lifestyle support is insufficient, but that is a clinician decision.

A practical plan

First, confirm the number and context. Ask whether the result was HbA1c or fasting glucose, what unit was used, and whether anything could distort HbA1c. If HbA1c is 42 to 47 mmol/mol, ask when it should be repeated, whether you are eligible for Healthier You, and whether blood pressure, lipids, kidney function and liver health should be reviewed at the same time.

Second, choose 2 or 3 measurable levers for 12 weeks. Examples: walk 10 minutes after the largest meal most days, add 2 resistance sessions per week, replace sugary drinks and juice, build breakfast around protein and fibre, reduce late-night snacks, or set a bedtime that is actually possible. Recheck HbA1c after enough time for change to show, usually around 3 months if your clinician agrees.

Third, avoid false precision. A continuous glucose monitor can be educational for some people, but it is not required to diagnose prediabetes and can make healthy people over-focus on normal post-meal rises. Use the ApoB and lipid panel guide if your glucose risk sits with high triglycerides or cholesterol, start here to organise symptoms and results, insights to challenge glucose-spike marketing, and the stack builder before mixing supplements with prescribed medicines.

This article is educational and does not constitute medical advice, diagnosis, or a treatment recommendation. Medication uses described as “off-label” are not licensed for that purpose in the UK and should only be considered under qualified clinical supervision. Always speak to your GP, pharmacist, or a registered specialist before starting, stopping, or changing any treatment. If you have severe or alarm symptoms - unintentional weight loss, blood in your stool, difficulty swallowing, persistent vomiting, a fever, or severe pain - seek urgent medical care.