HbA1c Explained

This page describes what the blood test known as HbA1c is, and how it is useful in monitoring diabetes.


 In 2009, the way in which HbA1c results were reported in the UK changed from % to mmol/mol. 

What is HbA1c?

Glucose (blood glucose) in the blood sticks to haemoglobin in red blood cells, making glycosolated haemoglobin, called haemoglobin A1c or HbA1c. Red blood cells live for about 8 - 12 weeks before being replaced so the HbA1c test tells you how well controlled your blood glucose has been over the previous 8 - 12 weeks (2-3 months).The more glucose in your blood, the more HbA1c will be present, so the level reported will be higher.

What does it tell us?

The better your blood glucose control the less chance there is of you developing diabetes complications such as eye, kidney or nerve damage, heart disease or stroke.  The HbA1c test tells you whether you are on target to keep your risk of complications as low as possible.

Why measure HbA1c? 

Because blood glucose levels vary throughout the day and from day to day, HbA1c is usually measured every 3-6 months. The results show if your blood glucose control has altered in response to changes in your diet, physical activity or medication.

HbA1c results and targets

For most HbA1C results used to be given just as a percentage. It is important that you agree your own individual target with your health care team, as sometimes a different target might be more appropriate. For example, if you have had a lot of problems with low blood glucose levels (hypos), a higher target might be appropriate.

What has changed?

Laboratories in the UK have changed the way in which HbA1C is reported. The International Federation of Clinical Chemistry (IFCC) have a new reference measurement method after discussion with diabetes groups worldwide. This will make comparing HbA1c results from different laboratories and from research trials throughout the world much easier. The fact that the number is higher does not mean there is more glucose in your blood. It is just a different way of expressing the same thing.

What are the IFCC HbA1c results? 

The measurement will be in millimoles per mol (mmol/mol) instead of percentage (%)

Here is how the results compare: 

HbA1c (DCCT)

HbA1c (IFCC)





















Old method

New method

 You may also be interested in more information on HbA1C targets and home blood glucose testing/targets, you can find more information on this here

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