HbA1c refers to glycated haemoglobin — the amount of glucose that's attached to the haemoglobin (a protein found in red blood cells). An HbA1c blood test is used as a way to measure your average blood sugar levels over the past 3 months. This can help indicate your risk of developing diabetes. A healthy lifestyle can help lower raised HbA1c levels.

What is HbA1c?

HbA1c refers to glycated haemoglobin — how much glucose is attached to the haemoglobin (a protein found in red blood cells). It's sometimes called haemoglobin A1c or just A1c.

What is an HbA1c test?

When the sugar in your blood rises, it binds to haemoglobin in your red blood cells. And because your red blood cells live for about 3 months, an HbA1c blood test can tell your average blood glucose (sugar) control over the last 3 months. This helps indicate your pre-diabetes and diabetes risk.

You can check your blood sugar control at home by using an HbA1c blood test.

Is an HbA1c test suitable for everyone?

An HbA1c test won’t tell you how high your blood sugar is. But it can tell you if your blood sugar has been high over the last 3 months. Some conditions can cause fluctuations in your HbA1c levels. 

A doctor won't use this type of test if diagnosing diabetes. This includes if you:

  • are pregnant or gave birth in the last 2 months
  • have only been experiencing diabetes symptoms for 2 months — like frequent urination or excessive thirst
  • take medication that can affect your blood sugar levels — like long-term steroid treatment and some antibiotics
  • are currently acutely ill (a sudden and severe sickness)
  • have pancreatic problems
  • have end-stage kidney disease
  • are HIV positive

If you have one of these conditions, it's better to speak with your GP, who'll most likely organise an oral glucose tolerance test instead. This test checks your glucose levels after you've fasted and then after you've had a sugary drink — shows how well your body handles glucose.

Some health conditions can make it more difficult to interpret your HbA1c results — for example, if you've had a recent blood transfusion.

What's a normal HbA1c level?

The ranges for HbA1c levels are defined as:

  • normal range = below 42 mmol/mol
  • prediabetes = 42-47 mmol/mol
  • indicates diabetes = 48 mmol or over

What does a high HbA1c level mean?

An HbA1c test can help indicate your risk of developing pre-diabetes and type 2 diabetes — if you don't have any condition that might affect your results. Or if you have diabetes, an HbA1c test is a useful way to check how well you're controlling your blood sugar levels.

Symptoms of high HbA1c levels

If your HbA1c result indicates pre-diabetes, it's unlikely you'll have any symptoms. But if your HbA1c level indicates diabetes, some common symptoms include:

  • increased thirst
  • frequent urination
  • tiredness
  • blurred vision

If you have any of these symptoms, you should see your doctor.

Long-term, a high HbA1c result might lead to things like eye problems, kidney disease, and nerve damage.

What can cause a high HbA1c level?

A number of things can cause high blood sugar levels and subsequently high HbA1c levels. These include:

  • being overweight
  • an unhealthy diet
  • lack of exercise
  • chronic stress
  • some medications — for example, steroids
  • diabetes

How to lower your HbA1c level

There are lots of ways to lower your HbA1c levels, including:

  • exercising regularly
  • losing weight if you’re overweight
  • choosing carbohydrates with a low glycaemic index (GI) — like whole grains, pulses, some fruit and vegetables
  • avoiding processed foods high in trans and saturated fats and sugar
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Diabetes UK (2018). What is HbA1c?. Retrieved 25 April 2019 from https://www.diabetes.org.uk/guide-to-diabetes/managing-your-diabetes/hba1c.

National Health Services (2017). Type 2 diabetes: Getting diagnosed. Retrieved 25 April 2019 from https://www.nhs.uk/conditions/type-2-diabetes/getting-diagnosed/.

NICE (2021). When should I suspect type 2 diabetes in an adult? Retrieved 17 August 2021 from https://cks.nice.org.uk/topics/diabetes-type-2/diagnosis/diagnosis-in-adults/.

WHO (2011). Use of Glycated Haemoglobin (HbA1c) in the Diagnosis of Diabetes Mellitus. Retrieved 17 August 2021 from https://www.who.int/diabetes/publications/report-hba1c_2011.pdf.