HbA1c for controlled diabetes is one of the most important measures your GP or diabetes team will use to assess how well your blood sugar has been managed over the preceding two to three months. Expressed in mmol/mol or as a percentage, this blood test reflects the proportion of haemoglobin that has become glycated — offering a far more reliable picture of longer-term glucose control than a single finger-prick reading. Whether you have Type 1 or Type 2 diabetes, understanding your HbA1c target, what influences your result, and how to act on it are all essential steps towards reducing your risk of serious complications.

What HbA1c Measures and Why It Matters in Diabetes

HbA1c measures the proportion of glycated haemoglobin in red blood cells, reflecting average blood glucose over the preceding two to three months and providing a reliable indicator of longer-term diabetes control.

HbA1c — formally known as glycated haemoglobin — is a blood test that reflects your average blood glucose levels over the preceding two to three months. When glucose circulates in the bloodstream, it binds irreversibly to haemoglobin, the protein found inside red blood cells. Because red blood cells have a lifespan of approximately 120 days, the proportion of haemoglobin that has become glycated provides a reliable snapshot of longer-term glucose control, rather than a single moment in time. It is worth noting that HbA1c is a time-weighted average, meaning it is more heavily influenced by glucose levels in the most recent six to eight weeks than by those earlier in the period.

This makes HbA1c particularly valuable in diabetes management. Unlike a finger-prick glucose reading, which can fluctuate significantly depending on meals, stress, or physical activity, HbA1c offers a more stable and objective measure of how well blood sugar has been managed over weeks. It is expressed either as a percentage or in millimoles per mole (mmol/mol), with the latter being the standard unit used across NHS laboratories in the UK.

For people living with either Type 1 or Type 2 diabetes, HbA1c is central to:

• Assessing whether current treatment is effective

• Identifying the risk of long-term complications such as retinopathy, nephropathy, and cardiovascular disease

• Guiding decisions about medication adjustments

It is important to understand that HbA1c is not a perfect measure for everyone. Certain conditions — discussed later in this article — can affect its accuracy. Nevertheless, for the majority of people with diabetes, it remains the cornerstone of monitoring and one of the most clinically meaningful indicators of controlled diabetes.

Further information: NHS: HbA1c (Glycated haemoglobin) test; Lab Tests Online UK (ACB): HbA1c overview.

NICE Guidelines for HbA1c Targets in Controlled Diabetes

NICE recommends an HbA1c target of 48 mmol/mol (6.5%) for Type 2 diabetes managed without hypoglycaemia-risk drugs, and 53 mmol/mol (7.0%) for those on sulphonylureas or insulin; targets should always be personalised.

The National Institute for Health and Care Excellence (NICE) provides clear, evidence-based guidance on HbA1c targets for people with diabetes, recognising that optimal targets may differ depending on the type of diabetes, treatment regimen, and individual circumstances.

For Type 2 diabetes, NICE guidance (NG28) recommends the following targets:

• 48 mmol/mol (6.5%) for people managed by diet alone or with a single non-hypoglycaemia-inducing drug such as metformin

• 53 mmol/mol (7.0%) for those on medications that carry a risk of hypoglycaemia, such as sulphonylureas or insulin

NICE NG28 also advises that if HbA1c rises to 58 mmol/mol (7.5%) or above, treatment should be reviewed and intensified where appropriate, in discussion with the patient.

For Type 1 diabetes, NICE guidance (NG17) recommends a target of 48 mmol/mol (6.5%) where this can be achieved safely without problematic hypoglycaemia. NICE acknowledges that individual targets should be agreed collaboratively between the patient and their clinical team, taking into account quality of life, hypoglycaemia awareness, and comorbidities. Where continuous glucose monitoring (CGM) is used, time-in-range data may complement HbA1c in assessing overall glucose control.

It is worth noting that stricter targets are not always better. Pursuing very low HbA1c levels can increase the risk of hypoglycaemia, which carries its own serious health risks. Conversely, consistently elevated HbA1c — generally above 58 mmol/mol (7.5%) — is associated with a significantly higher risk of microvascular and macrovascular complications over time.

NICE also highlights that targets should be personalised, particularly for older adults, those with frailty, or individuals with a history of cardiovascular disease, where less stringent targets may be more appropriate and safer. Always discuss your individual target with your GP or diabetes specialist.

References: NICE NG28: Type 2 diabetes in adults; NICE NG17: Type 1 diabetes in adults.

Factors That Can Affect Your HbA1c Reading

Conditions such as haemolytic anaemia, iron deficiency, haemoglobin variants, and advanced CKD can cause falsely low or falsely high HbA1c results, making alternative monitoring methods necessary in some patients.

Whilst HbA1c is a robust and widely used measure, several physiological and medical factors can influence its accuracy, potentially leading to falsely high or falsely low results. Being aware of these factors is important for both patients and clinicians when interpreting results.

Conditions that may cause a falsely low HbA1c include:

• Haemolytic anaemia, where red blood cells are destroyed more rapidly than usual, reducing the time available for glycation

• Recent blood transfusions — HbA1c results are generally unreliable for up to three months following a transfusion, as the effect on the reading is unpredictable and depends on the donor blood and storage conditions

• Haemoglobin variants such as sickle cell trait or haemoglobin C disease — the precise effect depends on the assay method used by your local laboratory

• Advanced chronic kidney disease (CKD), where reduced red blood cell lifespan and the effects of erythropoietin or iron therapy often lead to a falsely low result

Conditions that may cause a falsely high HbA1c include:

• Iron deficiency anaemia (before treatment), as older red blood cells accumulate and carry more glycated haemoglobin

• Vitamin B12 or folate deficiency

• Splenectomy (removal of the spleen), which prolongs red blood cell lifespan

It is important to note that in CKD, the effect on HbA1c can be variable and is often in the direction of a falsely low reading, particularly in advanced disease. If you have CKD, your clinical team may recommend alternative monitoring approaches such as capillary blood glucose profiles or CGM.

Certain medicines are known to affect HbA1c results. Those with the strongest evidence include dapsone, ribavirin, interferon, and hydroxyurea, which can cause haemolysis and lead to falsely low readings. If you are taking any of these medicines, inform your diabetes team so that results can be interpreted with appropriate caution.

Pregnancy is another important consideration. HbA1c is not recommended as the primary method of monitoring glycaemia during pregnancy. Altered red blood cell dynamics in pregnancy make results unreliable for routine monitoring; capillary blood glucose testing and CGM are preferred. HbA1c may be used at booking and around 28 weeks to help assess risk, in line with NICE guidance (NG3).

If your clinical team suspects that your HbA1c result may not accurately reflect your glucose control, they may recommend alternative tests such as fructosamine or more frequent self-monitoring of blood glucose. Always inform your healthcare provider of any relevant medical history or recent changes in your health.

References: Lab Tests Online UK (ACB): HbA1c interferences; UK Kidney Association: Diabetes management in CKD; NICE NG3: Diabetes in pregnancy; NHS: HbA1c test.

How Often Should You Have an HbA1c Test on the NHS

NICE recommends HbA1c testing every six months for people with well-controlled, stable diabetes, and every three months for those not yet at target or following a recent medication change.

The frequency of HbA1c testing on the NHS is guided by NICE recommendations and tailored to the individual's current level of diabetes control, treatment regimen, and clinical stability.

For people with well-controlled diabetes who are on a stable treatment plan and meeting their agreed HbA1c target, NICE recommends testing every 6 months. This interval allows sufficient time to detect meaningful changes in glucose control whilst avoiding unnecessary testing.

For those whose diabetes is not yet at target, who have recently changed medication, or who are experiencing fluctuating glucose levels, more frequent testing — typically every 3 months — is recommended until stability is achieved. This more intensive monitoring helps clinicians make timely adjustments to treatment.

In Type 1 diabetes, NICE guidance (NG17) suggests HbA1c should be measured at least every 3 to 6 months, depending on individual circumstances and clinical need. People using insulin pump therapy or continuous glucose monitoring may have their monitoring schedule adapted accordingly.

During pregnancy, HbA1c has a limited role in routine monitoring. Testing intervals and methods follow NICE NG3, with capillary blood glucose and CGM being the preferred approaches.

It is also worth noting that HbA1c testing forms part of the NHS Diabetes Annual Review, a structured check-up that all people with diabetes should receive each year. This review encompasses a range of assessments including blood pressure, kidney function, cholesterol, foot examination, and eye screening — all of which contribute to a comprehensive picture of diabetes management.

If you are unsure how often you should be tested, or if you feel your diabetes control has changed between scheduled appointments, do not hesitate to contact your GP surgery or diabetes care team. Proactive communication is an important part of staying in control.

References: NICE NG28: Type 2 diabetes in adults; NICE NG17: Type 1 diabetes in adults; NICE NG3: Diabetes in pregnancy; NHS: Your annual diabetes care review.

What to Do If Your HbA1c Is Within or Outside Your Target Range

An HbA1c within target indicates effective management; if above target, treatment review and possible intensification are warranted, while a result below target may signal hypoglycaemia risk requiring prompt medication review.

Receiving your HbA1c result can prompt different responses depending on whether it falls within or outside your agreed target range. Understanding what each scenario means — and what steps to take — can help you remain actively engaged in your own care.

If your HbA1c is within your target range, this is a positive indicator that your current management plan is working effectively. You should:

• Continue with your current diet, physical activity, and medication regimen

• Attend all scheduled reviews and monitoring appointments

• Remain vigilant for symptoms of hypoglycaemia or hyperglycaemia, even when overall control appears good

• Discuss with your team whether any lifestyle adjustments could further support your long-term health

If your HbA1c is above your target range, this suggests that blood glucose levels have been consistently higher than ideal. This does not necessarily mean your diabetes is out of control, but it does warrant a review. Your GP or diabetes team may consider:

• Reviewing your diet and physical activity habits

• Adjusting the dose or type of medication

• Introducing additional therapies in line with NICE guidance — for example, an SGLT-2 inhibitor (particularly where there is established cardiovascular disease, heart failure, or CKD) or a GLP-1 receptor agonist (particularly where weight management or cardiovascular risk reduction is a priority); your team will assess which options are appropriate for you individually

• Referring you to a structured education programme such as DESMOND or X-PERT (for Type 2) or DAFNE (for Type 1), as recommended by NICE

• Considering specialist referral if control remains persistently poor or if insulin initiation or complex management is required

If your HbA1c is below your target range, whilst this may initially seem reassuring, it can indicate a risk of hypoglycaemia, particularly if you are on insulin or a sulphonylurea. Contact your GP or diabetes nurse promptly if you are experiencing frequent low blood sugar episodes, as your medication may need to be reduced.

When to seek urgent help: If you experience symptoms that may suggest a hyperglycaemic crisis — such as abdominal pain, vomiting, rapid or laboured breathing, drowsiness, or severe dehydration — call 999 or go to your nearest emergency department immediately, as these may indicate diabetic ketoacidosis (DKA) or hyperosmolar hyperglycaemic state (HHS). Likewise, seek same-day urgent medical attention for any severe or recurrent hypoglycaemic episode that does not resolve with standard treatment.

Not sure if this is normal? Chat with one of our pharmacists →

If you experience suspected side effects from any diabetes medication, you can report these directly to the MHRA via the Yellow Card Scheme at yellowcard.mhra.gov.uk or through the Yellow Card app.

References: NICE NG28: Type 2 diabetes in adults (treatment intensification); NICE NG17: Type 1 diabetes in adults; MHRA Yellow Card Scheme.

Working With Your GP or Diabetes Team to Maintain Good Control

Sustained HbA1c control requires ongoing collaboration with your GP and diabetes team, combining person-centred care, structured education programmes such as DESMOND or DAFNE, lifestyle measures, and timely medication review.

Achieving and sustaining a healthy HbA1c for controlled diabetes is rarely the result of medication alone — it is the product of an ongoing, collaborative relationship between you and your healthcare team. In the UK, diabetes care is typically delivered through a combination of GP-led management, specialist diabetes nurses, dietitians, and, where needed, hospital-based diabetes consultants.

Open and honest communication with your team is essential. If you are finding it difficult to manage your diet, experiencing side effects from medication, or struggling with the emotional burden of diabetes — sometimes referred to as diabetes distress — these are all valid concerns that your team can help address. NICE guidance emphasises the importance of person-centred care, meaning your values, preferences, and lifestyle should be central to any management decisions.

Experiencing these side effects? Our pharmacists can help you navigate them →

Practical steps to support good HbA1c control include:

• Following a balanced diet, with guidance from a registered dietitian if needed

• Engaging in regular physical activity — even moderate exercise such as brisk walking can meaningfully improve insulin sensitivity

• Taking medications as prescribed and reporting any concerns about side effects promptly; suspected side effects can also be reported via the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk)

• Attending all scheduled diabetes reviews and screening appointments

• Using self-monitoring of blood glucose where recommended, particularly if you are on insulin

NICE recommends that all people with diabetes have access to a structured education programme. For Type 2 diabetes, this includes programmes such as DESMOND and X-PERT; for Type 1 diabetes, DAFNE is the established option. Ask your GP or diabetes team about referral if you have not yet attended one of these programmes.

Digital tools and NHS-approved apps can also support self-management between appointments. The NHS App provides access to health records and appointment management. If you are at high risk of developing Type 2 diabetes but have not yet been diagnosed, the NHS Diabetes Prevention Programme (NDPP) offers evidence-based support — however, please note that this programme is designed for people with non-diabetic hyperglycaemia (raised blood sugar that has not yet reached the threshold for a diabetes diagnosis), not for those already living with diabetes.

Consider contacting your GP or diabetes team promptly — rather than waiting for your next scheduled review — if you experience any of the following: recurrent severe hypoglycaemia or hypoglycaemia unawareness; persistent poor glucose control despite treatment; unexplained weight loss or ketones in your urine; symptoms of DKA or HHS (see above); or if you are pregnant or planning a pregnancy. Early intervention consistently leads to better outcomes in diabetes management.

References: NICE NG28: Education and self-management support; NICE NG17: Structured education for Type 1 diabetes; NHS Diabetes Prevention Programme (eligibility criteria); Diabetes UK: Structured education programmes and care checks; MHRA Yellow Card Scheme.

Frequently Asked Questions