HbA1c test – diagnosing diabetes and pre-diabetes

Key points about HbA1c testing

  • The HbA1c test measures your average blood glucose (sugar) levels over 3 months.
  • It is used in 2 ways – to diagnose type 2 diabetes, and to check your blood glucose levels if you have already been diagnosed with type 2 diabetes.
  • The HbA1c test involves taking a sample of blood.
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HbA1c is what’s known as glycated haemoglobin. Haemoglobin (Hb) is the protein in your blood that carries oxygen around your body.

Glucose (a type of sugar) in your blood can stick to the haemoglobin protein. When this happens the haemoglobin is called glycated haemoglobin or HbA1c. The higher the glucose (sugar) levels are in your blood, the more of it attaches to your haemoglobin and the higher your HbA1c level is.

The HbA1c test measures the amount of glucose that has built up in your blood over a 3-month period. HbA1c testing is different from the glucose test (usually finger prick) that is used to tell you what your level is right now, due to things like exercise, medicines and what you eat. An HbA1c test is done to assess your blood glucose control over a longer 3-month period and to check how well your lifestyle measures such as diet and exercise, together with your diabetes medicines, are working to control your diabetes.

The HbA1c test involves taking a sample of blood. It can be done at any time of the day. It doesn't matter whether you have eaten or not.

The HbA1c test is used to diagnose pre-diabetes and type 2 diabetes. It is reported as millimoles per mole (mmol/mol).

Normal HbA1c

A result of 40 mmol/mol or lower is normal for people without diabetes or pre-diabetes.

Diagnosing prediabetes

Pre-diabetes is when the amount of sugar in your blood is higher than normal. An HbA1c level between 41-49 mmol/mol indicates you have prediabetes (also called impaired glucose tolerance or IGT) which means you are at much higher risk of getting type 2 diabetes and heart disease. 

Finding out you have prediabetes can be a chance to make changes. You may be able to stop it progressing to type 2 diabetes and increasing your risk of heart disease by making lifestyle changes. Read more about prediabetes.

Diagnosing type 2 diabetes

If you have symptoms of diabetes (such as excessive thirst, frequent peeing, or recurrent infections), only one high HbA1c result (50 mmol/mol or higher) is needed to confirm the diagnosis.

If you do not have symptoms of diabetes, two high HbA1c results (50 mmol/mol or higher) are needed to confirm the diagnosis.

Once you have diabetes, you have it for life. But early treatment, including having a healthy lifestyle, can help to reduce damage to your eyes, kidneys, heart, feet and brain. Read more about type 2 diabetes.

Diagnosis HbA1c level
Normal 40 mmol/mol or below
Pre-diabetes 41–49 mmol/mol

50 mmol/mol or above

If you have been diagnosed with type 2 diabetes, the HbA1c test is also used to monitor your diabetes and to check how well controlled your blood glucose (sugar) has been over the last 3 months. Read more about monitoring diabetes using HbA1c. 

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Credits: Healthify editorial team. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Dr Jeremy Tuohy

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