What is HbA1c?

Find out more about HbA1c, target levels, and what it can tell you about your blood sugar control.

If you have diabetes or are at risk of diabetes, you may have heard of the biomarker HbA1c. Or perhaps you’ve come across it as part of a health check-up and you’d like to learn more. Either way, this article can help you understand what HbA1c is and what it might mean for your health.  

In this article, we cover:  

What is HbA1c?

An HbA1c test measures your average blood sugar levels over the past two to three months.  

HbA1c stands for glycated haemoglobin. Haemoglobin is a protein in the blood that carries oxygen to the tissues. When blood sugar levels are high, glucose (a type of sugar) binds to haemoglobin to form glycated haemoglobin or HbA1c. The higher your blood sugar levels, the more HbA1c is present in the blood.  

Why do I need an HbA1c blood test?

An HbA1c test is used to check for and monitor diabetes, or to assess how well you’re responding to diabetes medication. It’s a useful screening tool since it measures your average blood sugar level over a long period rather than at a single point in time (unlike a blood glucose test).  

Good HbA1c control is known to lower your risk of complications related to diabetes. 

What is a normal HbA1c level?

HbA1c can either be expressed as a percentage or as mmol/mol. Since 2009, the default unit for the UK is mmol/mol.  

For most people, it’s best to aim for an HbA1c below 42 mmol/mol (6%).  

If you have diabetes, your healthcare team will talk to you about your target level as it will be unique. Generally, with diabetes, an ideal target HbA1c level is less than 48 mmol/mol (6.5%), but this might be unrealistic for some people. Your target may change over time depending on your blood sugar control and any complications you may have.  


HbA1c  mmol/mol % 
Normal  <42 <6
Pre-diabetes 42–47 6–6.4
Diabetes  48 6.5 


Does HbA1c confirm diabetes?

An HbA1c of 48mmol/mol (6.5%) is recommended as the cut-off for diagnosing diabetes. However, a value less than this does not necessarily exclude diabetes, and a raised HbA1c doesn’t always mean you have diabetes. A fasting plasma glucose concentration (with different cut-off thresholds) is also sometimes used to help confirm the diagnosis of diabetes.  

HbA1c may be falsely lowered in the following conditions [1]:  

  • Haemolysis (red blood cell breakdown) 
  • Haemoglobinopathies (such as thalassaemia) 
  • Recent blood transfusion 
  • Chronic liver disease 
  • Certain medications (antiretroviral drugs) 

HbA1c may be falsely raised in the following conditions: 

  • Iron deficiency 
  • Vitamin B12 deficiency 
  • Excess alcohol 
  • Raised bilirubin 

Diabetes is usually accompanied by symptoms. Where it’s not, the blood test should be repeated to confirm the result.  

HbA1c is not appropriate to diagnose diabetes in [2]:  

  • Children and young people 
  • People with suspected type 1 diabetes 
  • People with symptoms of diabetes for less than two months 
  • People who are acutely ill 
  • People taking medications that may cause rapid changes in glucose levels (e.g. steroids) 
  • People with acute pancreatic damage or surgery 
  • Pregnancy 
  • People with genetic conditions that may influence HbA1c and its measurement 

If you’re concerned you may have diabetes, you should speak to your doctor who can investigate your symptoms appropriately.  

How often should I check HbA1c?

Everyone with diabetes should be offered an HbA1c test at least once every six months [3].  

You may need more frequent HbA1c tests if: 

  • You’ve recently been diagnosed with diabetes 
  • Your HbA1c is unstable 
  • You’ve made changes to your diabetes medications 
  • You’re unwell or have other health conditions 

If you don’t have diabetes or other health conditions and are in the 40 to 74 age group, you’ll be offered an HbA1c test as part of an NHS Health Check. You’ll be invited to repeat this check-up every five years. If you’re at greater risk of diabetes or have pre-diabetes, it’s likely your doctor will advise an HbA1c more frequently.  

How can I check my HbA1c level from home?

You can test your HbA1c level with our Diabetes (HbA1c) Blood Test. We send an HbA1c test kit to your home which you can take yourself as a finger-prick test. Alternatively, you can arrange to have a venous sample taken.  

Once you’ve sent your kit back to us, one of our doctors will provide you with a written report which includes any next steps you should take.  

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What happens when HbA1c is high?

If your HbA1c is raised, it’s likely your blood sugar levels have been consistently high over the past few months.  

A higher HbA1c puts you at greater risk of complications of diabetes, including:  

  • Cardiovascular disease —increasing the risk of heart attack and stroke 
  • Kidney disease — which can ultimately lead to kidney failure if it’s not corrected 
  • Neuropathy — leading to numbness or altered sensation in the hands and feet 
  • Retinopathy — which can cause visual loss or blindness if left untreated 

You can minimise these risks by maintaining good blood sugar control through a healthy diet, exercise, and weight loss.

Can HbA1c go back to normal?

Successfully reversing type 2 diabetes is known as going into remission. This is achievable by bringing your blood sugar levels below the diabetes range. Diabetes is mainly put into remission by substantial weight loss in people who are overweight. 

There’s not enough evidence that remission is permanent – it needs to be maintained. Unfortunately, it’s not yet possible to bring type 1 diabetes into remission, but scientists are looking into how this might be possible in future. 

Find out more about diabetes remission.  

What’s the fastest way to reduce HbA1c?

There are many things you can do to help keep your HbA1c level in check. A combination of techniques is more effective than just one.  

Here are seven tips to reduce your HbA1c: 

  • Get regular exercise — even light exercise, if carried out regularly, can improve your blood sugar control as well as help you to lose weight. 
  • Lose weight if you’re overweight — being overweight leads to insulin resistance which makes it more difficult for your body to control blood sugar levels effectively 
  • Get good sleep – research shows that poor sleep quality, or not getting enough or too much sleep, is associated with higher Hba1c levels [4]. 
  • Be restaurant-savvy — many restaurants contain hidden sugars in their menus. Try replacing carbohydrate sides with a salad or look up the menu beforehand.  
  • Know how to de-stress — have some methods up your sleeve for stressful times. Chronic stress leads to poorer blood sugar control.  
  • Eat to your meter — if you have diabetes, regularly measuring your blood sugar levels before and after meals can help you learn which foods are likely to cause a spike in your blood sugar levels.  
  • Cut down on alcohol — many alcoholic drinks, like beer, contain a lot of calories which can lead to weight gain and raised HbA1c. 

More information on HbA1c and diabetes 

There are lots of great resources on HbA1c, diabetes, and how you can prevent the condition. Visit Diabetes UK or the NHS website to find out more.  



  1. Unnikrishnan R, Anjana RM, Mohan V. Drugs affecting HbA1c levels. Indian J Endocrinol Metab. 2012;16(4):528–31.
  2. Diagnostic criteria for diabetes [Internet]. Diabetes UK. [cited 2022 Dec 30]. Available from: https://www.diabetes.org.uk/professionals/position-statements-reports/diagnosis-ongoing-management-monitoring/new_diagnostic_criteria_for_diabetes
  3. Type 2 diabetes - Going for regular check-ups [Internet]. nhs.uk. 2018 [cited 2022 Dec 30]. Available from: https://www.nhs.uk/conditions/type-2-diabetes/going-regular-check-ups/
  4. Nakajima H, Kaneita Y, Yokoyama E, Harano S, Tamaki T, Ibuka E, et al. Association between sleep duration and hemoglobin A1c level. Sleep Med. 2008 Oct;9(7):745–52.