HbA1c and Pre-diabetes: What Your Blood Sugar Test Really Means
- Dr James Coleman
- Mar 26
- 5 min read
Pre-diabetes means your blood sugar levels are higher than normal but not yet high enough to be classified as type 2 diabetes. Around 6.3 million adults in the UK have been identified with raised blood sugar levels, according to Diabetes UK. Many of them don't know it, because pre-diabetes rarely causes obvious symptoms.
The good news is that pre-diabetes is reversible. With the right lifestyle changes, most people can bring their blood sugar back into the normal range and significantly reduce their risk of progressing to type 2 diabetes. But you can't act on something you don't know about, which is where HbA1c testing comes in.
What Is HbA1c?
HbA1c (glycated haemoglobin) measures how much glucose has attached to the haemoglobin in your red blood cells over their approximately 120-day lifespan. This gives an average picture of your blood sugar control over the previous two to three months, making it much more informative than a single fasting glucose reading, which only captures one moment in time.
The test doesn't require fasting, which is one of its practical advantages. Results are reported in mmol/mol, and the thresholds are well established [NICE PH38, 2012; updated 2017]:
Below 42 mmol/mol: normal
42 to 47 mmol/mol: pre-diabetes (also called non-diabetic hyperglycaemia)
48 mmol/mol or above: type 2 diabetes
These thresholds are defined by the World Health Organization and adopted in NICE guidance for diabetes prevention in the UK. For asymptomatic individuals, NICE recommends repeating the test to confirm a result before making a definitive diagnosis.
Why Pre-diabetes Matters
Pre-diabetes isn't a diagnosis to ignore. It tells you that your body is already struggling to regulate blood sugar effectively. Over time, the pancreas has to produce more and more insulin to keep glucose levels in check (a process called insulin resistance), and eventually it can't keep up. That's when blood sugar rises into the diabetic range.
A large UK Biobank study of over 330,000 individuals found that pre-diabetes was an independent risk factor for cardiovascular disease (conditions affecting the heart and blood vessels) and chronic kidney disease, even in people who never went on to develop full type 2 diabetes [Honigberg et al., Journal of the American College of Cardiology, 2021]. In other words, the metabolic changes happening during pre-diabetes carry their own health risks.
But progression is not inevitable. The NHS Diabetes Prevention Programme, which offers structured lifestyle support to people with pre-diabetes, has been independently evaluated and shown to reduce the risk of progressing to type 2 diabetes by approximately 20% through referral alone, and by 37% for those who complete the programme [Ravindrarajah et al., PLoS Medicine, 2023]. The main interventions are achievable: modest weight loss, increased physical activity, and dietary changes. In my experience, patients who understand their HbA1c result and what it means are far more motivated to make those changes.
What Can Affect Your HbA1c Result?
HbA1c is a reliable test for most people, but certain conditions can make the result less accurate. It's worth being aware of these:
Iron deficiency anaemia can falsely raise your HbA1c, because red blood cells live longer when iron is low, accumulating more glucose
B12 and folate deficiency can also increase red blood cell lifespan and produce a falsely elevated result
Conditions that destroy red blood cells faster than normal (such as haemolytic anaemia, where cells are broken down prematurely) can produce a falsely low HbA1c
Chronic kidney disease affects red blood cell turnover and can alter HbA1c accuracy
Pregnancy changes red blood cell dynamics, making HbA1c less reliable in the second and third trimesters
Haemoglobin variants, including sickle cell trait, may affect some laboratory testing methods
This is why your result should always be interpreted alongside your symptoms, risk factors, and other blood tests. A number on its own isn't the full picture.
Who Should Consider HbA1c Testing?
NICE recommends considering HbA1c testing if you have risk factors for type 2 diabetes [NICE PH38]. These include:
A body mass index (BMI) of 25 or above (23 or above for South Asian populations)
A family history of type 2 diabetes in a first-degree relative
A history of gestational diabetes
Polycystic ovary syndrome (PCOS)
South Asian, Black African, or African-Caribbean ethnicity
Age over 40 (or over 25 for high-risk ethnic groups)
If a previous HbA1c was normal but you still have risk factors, retesting every two to three years is reasonable. If your result was in the pre-diabetic range (42 to 47 mmol/mol), NICE recommends annual monitoring alongside lifestyle changes. Your GP can refer you to the NHS Diabetes Prevention Programme if you're eligible.
When to See Your GP
If your HbA1c comes back in the pre-diabetic range, your GP can discuss next steps including referral to the NHS Diabetes Prevention Programme. If your result is 48 mmol/mol or above, further assessment and potentially medication will be needed.
You should also see your GP if you're experiencing symptoms such as increased thirst, frequent urination, unexplained fatigue, blurred vision, or slow wound healing. These may indicate that diabetes has already developed.
How Brooksby Medical Can Help
Brooksby Medical offers HbA1c testing as part of several profiles, including the Diabetes Check and the Wellness Profile. A venous blood sample provides the accuracy needed for reliable HbA1c measurement. Every result comes with a GP-written report that interprets your level alongside your other results and risk factors.
If you have risk factors for type 2 diabetes and haven't had your HbA1c checked recently, it's a straightforward test that can tell you where things stand.
References
NICE. Type 2 diabetes: prevention in people at high risk. PH38 (2012, updated 2017). NICE PH38
Honigberg MC, Zekavat SM, Pirruccello JP, et al. Cardiovascular and kidney outcomes across the glycemic spectrum: insights from the UK Biobank. Journal of the American College of Cardiology. 2021;78(5):453-464
Ravindrarajah R, Sutton M, Reeves D, et al. Referral to the NHS Diabetes Prevention Programme and conversion from non-diabetic hyperglycaemia to type 2 diabetes mellitus. PLoS Medicine. 2023;20(2):e1004177
Diabetes UK. Number of people at risk of type 2 diabetes. Diabetes UK
Valabhji J, Barron E, Bradley D, et al. Early outcomes from the English National Health Service Diabetes Prevention Programme. Diabetes Care. 2020;43(1):152-160
NICE. Type 2 diabetes in adults: management. Guideline NG28 (2015, updated 2022). NICE NG28
Written by Dr James Coleman, GP and founder of Brooksby Medical. Dr Coleman is a practising General Practitioner who founded Brooksby Medical to give patients direct access to the blood tests and clinical interpretation they need, without waiting lists.
Medically reviewed: March 2026 | Next review due: March 2027
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Blood test results should always be interpreted by a qualified healthcare professional in the context of your individual symptoms, medical history, and clinical picture. If you have concerns about your health, please consult your GP.
