Why is my HbA1c going up? If your latest blood test has shown a rise, you are not alone — and understanding the reasons behind it is the first step to taking action. HbA1c reflects your average blood glucose over the past two to three months, making it one of the most reliable indicators of diabetes management. A rising result can stem from the natural progression of type 2 diabetes, lifestyle changes, certain medicines, or underlying health conditions. This article explains what drives HbA1c upwards, when to seek medical advice, and the evidence-based steps you can take — in partnership with your NHS care team — to bring it back towards your agreed target.

What HbA1c Measures and Why It Can Rise Over Time

HbA1c reflects average blood glucose over 8–12 weeks by measuring glucose bound to haemoglobin in red blood cells; a rising result indicates a sustained period of higher-than-target glucose levels.

HbA1c — glycated haemoglobin — is a blood test that reflects your average blood glucose levels over the preceding two to three months (approximately 8–12 weeks). When glucose circulates in the bloodstream, it binds irreversibly to haemoglobin inside red blood cells. Because red blood cells live for approximately 120 days, the HbA1c result gives clinicians a reliable window into longer-term glucose control, rather than a single snapshot in time.

In the UK, HbA1c is measured in millimoles per mole (mmol/mol) using IFCC-standardised methods. In line with WHO and NHS criteria, an HbA1c of 48 mmol/mol or above is used to diagnose type 2 diabetes; if you have no symptoms, a second confirmatory test is required. A reading between 42 and 47 mmol/mol indicates non-diabetic hyperglycaemia (sometimes called prediabetes). It is important to note that HbA1c is not suitable for diagnosis in certain situations — including pregnancy or within two months of giving birth, in children, where type 1 diabetes is suspected, or in people with conditions that affect red blood cell turnover (such as haemolytic anaemia, haemoglobinopathies, or following a recent blood transfusion).

For people already living with diabetes, HbA1c targets are agreed individually with your care team based on your circumstances, medicines, and risk of hypoglycaemia. Many adults with type 2 diabetes aim for 48 mmol/mol if their risk of hypoglycaemia is low; a target of 53 mmol/mol is often appropriate for those taking a sulphonylurea or insulin, where the risk of low blood glucose is higher. Less stringent targets may be agreed for people with frailty or significant comorbidities.

A rising HbA1c does not happen overnight — it reflects a gradual trend of higher blood glucose over weeks and months. This can occur even when you feel perfectly well, which is why regular monitoring is so important. Type 2 diabetes is a progressive condition, meaning that glucose control can become harder to maintain over time even without obvious changes in behaviour. Understanding why your HbA1c is climbing is the first step towards addressing it effectively and safely.

Common Reasons Your HbA1c May Be Increasing

The most common causes include the natural progression of type 2 diabetes, weight gain, reduced physical activity, dietary changes, illness, stress, and poor sleep; certain laboratory factors such as iron deficiency anaemia can also falsely raise the result.

There are several well-recognised reasons why HbA1c levels rise, and it is rarely due to a single cause. One of the most common explanations is the natural progression of type 2 diabetes itself. Over time, the pancreatic beta cells that produce insulin gradually lose their capacity to function effectively, meaning the body becomes less able to regulate blood glucose even with the same diet and medication regimen.

Other frequent contributors include:

• Weight gain, particularly around the abdomen, which increases insulin resistance

• Reduced physical activity, which lowers the muscles' ability to absorb glucose

• Changes in diet, such as increased intake of refined carbohydrates or sugary drinks

• Illness or infection, which triggers stress hormones that raise blood glucose

• Psychological stress, which can both directly raise glucose levels and indirectly affect self-care behaviours

• Poor sleep quality or sleep disorders, including obstructive sleep apnoea, which are associated with impaired glucose metabolism

It is also worth noting that certain laboratory or physiological factors can affect the accuracy of HbA1c readings. Iron deficiency anaemia tends to cause a falsely raised HbA1c, whilst haemolytic anaemias shorten red blood cell lifespan and may produce a falsely low result. Other conditions that can make HbA1c unreliable include chronic kidney disease or end-stage renal disease, recent blood transfusion, splenectomy, significant blood loss, and certain haemoglobin variants. HbA1c should not be used for diagnosis in pregnancy or within two months of giving birth.

Where HbA1c is considered unreliable, your clinical team may use an alternative measure such as fasting plasma glucose, an oral glucose tolerance test (OGTT), or — for monitoring purposes — fructosamine or glycated albumin. Always discuss unexpected results with your GP or diabetes nurse before drawing conclusions.

Lifestyle and Dietary Factors That Affect HbA1c Levels

High-glycaemic foods, reduced physical activity, and excess alcohol are key modifiable drivers of a rising HbA1c; UK guidelines recommend at least 150 minutes of moderate aerobic activity per week alongside a balanced, lower-refined-carbohydrate diet.

Diet plays a central role in blood glucose management, and changes in eating habits are one of the most modifiable reasons for a rising HbA1c. Foods with a high glycaemic index — such as white bread, white rice, sugary cereals, pastries, and sweetened beverages — cause rapid spikes in blood glucose. Over time, frequent consumption of these foods keeps average glucose levels elevated, which is directly reflected in a higher HbA1c.

Diabetes UK's evidence-based nutrition guidelines support a range of dietary approaches, provided they are nutritionally balanced and suited to individual preference, culture, and any other health conditions. These include Mediterranean-style, low-carbohydrate, and other patterns. General principles aligned with NHS and Diabetes UK guidance include:

• Choosing wholegrain carbohydrates over refined alternatives

• Increasing fibre intake through vegetables, pulses, and wholegrains

• Reducing portion sizes, particularly of starchy foods

• Limiting ultra-processed foods, takeaways, and foods high in added sugar

• Moderating alcohol consumption, as alcohol can cause unpredictable blood glucose fluctuations

Physical activity is equally important. Exercise improves insulin sensitivity and helps muscles use glucose more efficiently, both during and after activity. The UK Chief Medical Officers' Physical Activity Guidelines recommend that adults aim for at least 150 minutes of moderate-intensity aerobic activity per week, alongside muscle-strengthening activities on two or more days — advice that is consistent with NICE guidance for people with type 2 diabetes. Even modest increases in daily movement, such as walking after meals, can have a meaningful impact on glucose levels.

If you take a sulphonylurea or insulin, speak to your care team before significantly increasing your activity levels or reducing your carbohydrate intake, as these changes can increase the risk of hypoglycaemia (low blood glucose).

Smoking cessation is also relevant; smoking is associated with increased insulin resistance and a higher risk of diabetes complications. If you smoke, your GP can refer you to NHS Stop Smoking Services for support.

When to Speak to Your GP or Diabetes Care Team

Contact your GP or diabetes nurse promptly if your HbA1c is rising towards your agreed target, you have symptoms of high blood glucose, or you have started a new medicine affecting glucose; seek same-day urgent care if DKA or HHS is suspected.

A rising HbA1c should always prompt a conversation with your GP or diabetes care team, even if you feel well. In the UK, people with type 2 diabetes are typically offered an HbA1c check as part of their NHS diabetes annual review, but you should not wait for this appointment if you have concerns. When therapy is being adjusted, your care team will usually check your HbA1c every three to six months until it is stable.

Contact your GP or diabetes nurse promptly if:

• Your HbA1c is rising towards or above your agreed target, or shows a consistent upward trend

• You are experiencing symptoms of high blood glucose, such as increased thirst, frequent urination, fatigue, or blurred vision

• You have recently started a new medication that may affect glucose levels

• You have had a significant illness, surgery, or period of prolonged stress

• You are struggling to manage your diet, activity, or medication as previously agreed

Seek same-day urgent medical attention if you develop symptoms that could suggest diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS) — including rapid unexplained weight loss, vomiting, abdominal pain, deep or laboured breathing, drowsiness or confusion, or signs of severe dehydration. If you are pregnant or planning a pregnancy, inform your diabetes team promptly, as glucose targets and monitoring requirements differ significantly during pregnancy.

If your symptoms suggest possible type 1 diabetes — for example, rapid onset of thirst, weight loss, and fatigue, particularly in a younger person — seek urgent assessment, as this requires a different diagnostic and management approach.

For people newly diagnosed with non-diabetic hyperglycaemia (prediabetes), a rising HbA1c towards the diabetic range is a clear signal to seek review. Early intervention at this stage — through structured education programmes such as the NHS Diabetes Prevention Programme — can significantly reduce the risk of progression to type 2 diabetes.

Never adjust your diabetes medication without first speaking to a healthcare professional. Doing so can carry risks, including hypoglycaemia in those taking certain medicines such as sulphonylureas or insulin. Your care team can review your treatment plan safely and make evidence-based adjustments.

Medicines and Medical Conditions That Can Raise HbA1c

Corticosteroids, antipsychotics, thiazide diuretics, and some immunosuppressants are well-recognised causes of raised blood glucose; conditions such as Cushing's syndrome, PCOS, hypothyroidism, and chronic kidney disease can also impair glucose regulation.

Several medicines are known to raise blood glucose levels and, consequently, HbA1c. This does not necessarily mean the medication should be stopped — in many cases, the clinical benefit outweighs the metabolic effect — but it is important to be aware of the association and discuss it with your prescriber.

Medicines commonly associated with raised blood glucose include:

• Corticosteroids (such as prednisolone), which are widely used for inflammatory conditions and are a well-recognised cause of steroid-induced hyperglycaemia. Do not stop corticosteroids abruptly without medical advice.

• Antipsychotic medicines (such as olanzapine and clozapine), which can promote weight gain and insulin resistance. Do not stop these medicines without speaking to your prescriber.

• Some antihypertensives, including thiazide diuretics and beta-blockers, which may have modest, dose-dependent effects on glucose metabolism

• Immunosuppressants used after organ transplantation, such as tacrolimus

• Certain HIV antiretroviral therapies, particularly some protease inhibitors

Information on the metabolic effects of specific medicines can be found in the British National Formulary (BNF) and in the Summary of Product Characteristics (SmPC) for individual medicines, available via the electronic Medicines Compendium (eMC). MHRA and EMA guidance may also be relevant where drug safety updates have been issued.

Underlying medical conditions can also contribute. Cushing's syndrome (excess cortisol), polycystic ovary syndrome (PCOS), chronic kidney disease, hypothyroidism, and non-alcoholic fatty liver disease are all associated with impaired glucose regulation. Pancreatic conditions — including pancreatitis — can directly impair insulin production and cause blood glucose to rise. If you have unexplained weight loss, new-onset abdominal or back pain, or jaundice alongside a rising HbA1c, seek prompt medical review, as these can be red-flag symptoms requiring further investigation.

If you have recently started a new medicine and noticed a change in your glucose readings or HbA1c, raise this with your GP. Your prescriber can assess whether an alternative treatment or additional glucose-lowering support is appropriate. If you suspect a medicine is causing an adverse effect, you can report this via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

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Steps to Help Bring Your HbA1c Back Down Safely

Dietary review, gradual increases in physical activity, and medication adjustment guided by NICE NG28 are the main evidence-based approaches; SGLT-2 inhibitors and GLP-1 receptor agonists may be appropriate depending on individual cardiovascular and renal risk.

Bringing a rising HbA1c back towards your agreed target is achievable for most people, particularly when the underlying cause is identified and addressed. The approach should always be individualised and agreed with your healthcare team, as what works for one person may not be appropriate for another.

Dietary changes are often the most impactful first step. Working with a dietitian or diabetes specialist nurse to review your current eating patterns can help identify specific areas for improvement. The NHS Type 2 Diabetes Path to Remission Programme (a structured low-calorie diet programme) has demonstrated significant HbA1c reductions and, in some cases, remission of type 2 diabetes, supported by evidence from the DiRECT trial. Ask your GP whether you may be eligible.

Increasing physical activity gradually and safely is equally important. If you have not been active recently, start with short walks and build up over time. Your GP can refer you to an NHS exercise referral scheme if appropriate. If you take insulin or a sulphonylurea, discuss hypoglycaemia management with your care team before making significant changes to your activity levels.

Medication review may be necessary if lifestyle changes alone are insufficient. NICE guidance (NG28) on type 2 diabetes outlines a stepwise approach to glucose-lowering therapy. Metformin remains a common first-line option where tolerated. For people with established cardiovascular disease, heart failure, or chronic kidney disease, NICE and relevant technology appraisals support earlier use of SGLT-2 inhibitors (such as dapagliflozin or empagliflozin), which offer both glucose-lowering and organ-protective benefits. GLP-1 receptor agonists may be considered based on individual factors including weight, cardiovascular risk, and local formulary. Your care team will select medicines based on your specific clinical profile, comorbidities, and hypoglycaemia risk, without reference to any particular brand.

Self-monitoring of blood glucose at home is not routinely required for all people with type 2 diabetes, but is recommended when you are taking insulin or a sulphonylurea, during intercurrent illness, when medicines are being adjusted, or as agreed with your care team. Your team can advise on when and how to monitor, and what to do if readings are unexpectedly high or low.

Finally, attending your annual diabetes review and engaging with structured diabetes education — such as the DESMOND or X-PERT programmes — provides ongoing support and evidence-based strategies to help you manage your condition with confidence. If you suspect any medicine is causing an adverse effect, report it via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk).

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