HbA1c Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is HbA1c?

HbA1c, also known as glycated haemoglobin or haemoglobin A1c, is a blood marker that reflects your average blood sugar levels over the previous 8-12 weeks. It measures the percentage of haemoglobin — the oxygen-carrying protein in your red blood cells — that has become "glycated" (bonded with glucose).

Unlike a fasting glucose test, which provides a snapshot of your blood sugar at a single point in time, HbA1c gives a much broader picture of your long-term glucose control. This makes it an invaluable tool for both diagnosing diabetes and monitoring how well it is being managed.

The science behind HbA1c is straightforward: red blood cells have a lifespan of approximately 120 days. During this time, glucose in your bloodstream naturally attaches to haemoglobin molecules. The higher your average blood sugar, the more glucose binds to haemoglobin, and the higher your HbA1c reading will be. Because the test reflects an average over the red blood cell's lifespan, it is not affected by short-term fluctuations caused by individual meals, stress, or illness.

In the UK, HbA1c is reported in millimoles per mole (mmol/mol), although some international laboratories still use percentages. The NHS and NICE guidelines rely heavily on HbA1c for diabetes diagnosis and management targets.

Why Is HbA1c Tested?

HbA1c testing serves several critical clinical functions:

• Diabetes diagnosis: NICE and the World Health Organisation recommend HbA1c as a primary diagnostic tool for type 2 diabetes. An HbA1c of 48 mmol/mol (6.5%) or above on two separate occasions confirms a diabetes diagnosis.
• Pre-diabetes identification: An HbA1c between 42-47 mmol/mol (6.0-6.4%) indicates pre-diabetes (also called "non-diabetic hyperglycaemia"), a condition where blood sugar is elevated but not yet in the diabetic range. Early intervention at this stage can prevent progression to type 2 diabetes.
• Diabetes management monitoring: For people already diagnosed with diabetes, regular HbA1c testing (typically every 3-6 months) helps assess whether treatment — including medication, diet, and lifestyle changes — is effectively controlling blood sugar.
• Cardiovascular risk assessment: Elevated HbA1c is associated with increased risk of heart disease, stroke, and peripheral vascular disease, even in people without a formal diabetes diagnosis.
• Complication prevention: Maintaining HbA1c within target ranges significantly reduces the risk of diabetes-related complications, including retinopathy, nephropathy, neuropathy, and foot problems.
• Routine health screening: For individuals with risk factors such as obesity, family history of diabetes, polycystic ovary syndrome (PCOS), or a history of gestational diabetes, regular HbA1c testing enables early detection.

Normal Ranges

HbA1c results are reported in mmol/mol in the UK. The following table outlines the standard reference ranges used by the NHS:

Category	HbA1c (mmol/mol)	HbA1c (%)	Interpretation
Normal	Below 42	Below 6.0%	Healthy blood sugar control
Pre-diabetes	42 – 47	6.0 – 6.4%	At risk of developing type 2 diabetes
Diabetes	48 or above	6.5% or above	Diagnostic threshold for diabetes
Well-managed diabetes target	48 or below	6.5% or below	NICE target for most adults with type 2 diabetes
Type 1 diabetes target	48 or below	6.5% or below	NICE recommended target for type 1 diabetes

NICE recommends an individual target of 48 mmol/mol for most adults with type 2 diabetes managed by lifestyle and diet alone or with a single drug not associated with hypoglycaemia. For those on medications that carry a hypoglycaemia risk (such as sulphonylureas or insulin), the target may be adjusted to 53 mmol/mol (7.0%).

It is worth noting that HbA1c results can be unreliable in certain conditions that affect red blood cell turnover, including haemoglobin variants (such as sickle cell trait), iron deficiency anaemia, chronic kidney disease, and recent blood transfusions.

What Do High HbA1c Levels Mean?

An elevated HbA1c indicates that your average blood sugar has been higher than optimal over the past 2-3 months. Potential causes and associations include:

• Type 2 diabetes: The most common cause of persistently elevated HbA1c. Insulin resistance prevents cells from efficiently absorbing glucose from the bloodstream.
• Type 1 diabetes: Autoimmune destruction of insulin-producing beta cells in the pancreas leads to absolute insulin deficiency and high blood sugar.
• Pre-diabetes: Impaired glucose tolerance or impaired fasting glucose, representing an early stage in the progression towards type 2 diabetes.
• Poor dietary habits: A diet high in refined carbohydrates, sugary foods, and processed items can chronically elevate blood glucose levels.
• Physical inactivity: Sedentary behaviour reduces insulin sensitivity, meaning your body requires more insulin to manage the same amount of glucose.
• Medications: Certain drugs, including corticosteroids (such as prednisolone), some antipsychotics, and thiazide diuretics, can raise blood sugar levels.
• Polycystic ovary syndrome (PCOS): Insulin resistance is a hallmark feature of PCOS, and women with this condition are at significantly increased risk of developing type 2 diabetes.
• Cushing's syndrome: Excess cortisol production leads to increased glucose production and insulin resistance.

What Do Low HbA1c Levels Mean?

A low HbA1c (below 35 mmol/mol or 5.4%) is less commonly discussed but can have clinical significance:

• Frequent hypoglycaemia: In people with diabetes taking insulin or sulphonylureas, a very low HbA1c may indicate recurrent low blood sugar episodes, which can be dangerous.
• Haemolytic anaemia: Conditions causing premature destruction of red blood cells shorten their lifespan, reducing the time available for glycation and artificially lowering HbA1c.
• Significant blood loss: Recent haemorrhage or regular blood donation increases the proportion of younger red blood cells, which have had less exposure to glucose.
• Iron deficiency anaemia (treated): Following iron supplementation, a surge of new red blood cells can temporarily lower HbA1c readings.
• Chronic liver disease: Advanced liver disease can alter red blood cell metabolism and reduce HbA1c values.
• Chronic kidney disease with erythropoietin therapy: Treatment with erythropoietin stimulates red blood cell production, leading to a higher proportion of younger cells and lower HbA1c.
• Haemoglobin variants: Certain genetic haemoglobin variants (such as HbS, HbC, or HbE) can interfere with some HbA1c assays, producing falsely low or high results depending on the method used.
• Pregnancy: Physiological haemodilution and increased red blood cell turnover in pregnancy can lower HbA1c readings.

How to Improve Your HbA1c Levels

Reducing HbA1c is achievable through a combination of dietary changes, physical activity, and in some cases, medication. Here are evidence-based strategies:

Dietary Changes

• Reduce refined carbohydrates: Swap white bread, white rice, and sugary cereals for whole grains such as oats, quinoa, brown rice, and wholemeal bread. These have a lower glycaemic index and cause slower, more gradual rises in blood sugar.
• Increase fibre intake: Aim for at least 30g of fibre daily. Vegetables, legumes, nuts, seeds, and whole grains all contribute. Fibre slows glucose absorption and improves insulin sensitivity.
• Control portion sizes: Even healthy foods can raise blood sugar if consumed in excessive quantities. Using smaller plates and being mindful of carbohydrate portions at each meal can help.
• Prioritise protein and healthy fats: Including lean protein (chicken, fish, eggs, tofu) and healthy fats (olive oil, avocado, nuts) at each meal helps stabilise blood sugar and reduces post-meal glucose spikes.
• Limit sugary drinks: Fruit juices, fizzy drinks, and sweetened coffees can cause rapid blood sugar spikes. Water, herbal teas, and black coffee are better choices.

Physical Activity

• Aim for 150 minutes per week: The NHS recommends at least 150 minutes of moderate-intensity activity (brisk walking, cycling, swimming) per week. Regular exercise improves insulin sensitivity and helps lower HbA1c by 0.5-0.7% on average.
• Include resistance training: Strength exercises (weights, resistance bands, bodyweight exercises) 2-3 times per week build muscle mass, which increases glucose uptake from the bloodstream.
• Break up prolonged sitting: Standing or walking for 2-3 minutes every 30 minutes of sitting has been shown to reduce post-meal blood sugar levels.

Lifestyle Factors

• Achieve and maintain a healthy weight: Losing just 5-10% of body weight can significantly improve insulin sensitivity and reduce HbA1c. The NHS Diabetes Prevention Programme offers structured support for people with pre-diabetes.
• Prioritise sleep: Poor sleep quality and insufficient sleep (fewer than 7 hours) impair glucose metabolism. Aim for 7-9 hours of quality sleep per night.
• Manage stress: Chronic stress raises cortisol levels, which in turn increases blood sugar. Mindfulness, meditation, yoga, and regular physical activity can help manage stress.
• Stop smoking: Smokers have a higher risk of type 2 diabetes and poorer blood sugar control. The NHS offers free support through local stop smoking services.

When Should You Get Tested?

Regular HbA1c testing is recommended in the following situations:

• You are aged 40 or over and have not had a recent blood sugar check
• You have a family history of type 2 diabetes (parent or sibling)
• You are overweight or obese (BMI 25 or above, or 23 for South Asian individuals)
• You have been diagnosed with pre-diabetes and need monitoring (typically annually)
• You have polycystic ovary syndrome (PCOS)
• You had gestational diabetes during pregnancy
• You are of South Asian, African-Caribbean, or Black African descent (higher risk groups)
• You have existing diabetes and need regular monitoring (every 3-6 months)
• You experience symptoms such as excessive thirst, frequent urination, unexplained fatigue, or blurred vision

The NHS Health Check programme offers free HbA1c screening for adults aged 40-74 in England. If you fall outside this age range but have risk factors, proactive testing through a service like Lola Health provides peace of mind and early detection.

Which Lola Health Tests Include HbA1c?

HbA1c is one of the most important biomarkers we test at Lola Health. It is included in several of our comprehensive blood panels:

• Peak Insights — Our most comprehensive health assessment, including HbA1c alongside a full suite of metabolic, hormonal, and nutritional biomarkers.
• Vital Check — A detailed wellness panel that includes HbA1c to assess your blood sugar control and metabolic health.
• Core Health — Our essential health check, covering HbA1c and other foundational markers to give you a clear picture of your overall wellbeing.

All Lola Health tests use venous blood draws performed by qualified phlebotomists, ensuring medical-grade accuracy. Your results are reviewed by GP-certified professionals and come with personalised health recommendations tailored to your individual profile.