Diabetes – HbA1c readings

27 April 2014

HbA1c readings are used to determine how well your diabetes has been controlled over the last two to three months and, more recently, is also being used to diagnose diabetes.

What’s HbA1c?

HbA1c is a product that forms in the blood when glucose binds irreversibly to haemoglobin in the red blood cells.

The red blood cells have an average lifespan of two to three months so the HbA1c measure relates to the average blood glucose during that period.

Studies have shown that there’s an association between the HbA1c readings and the person’s risk of developing complications.

How’s it measured?

In the UK, and some other parts of the world, the DCCT aligned HbA1c values were used to report HbA1c readings, expressed as % haemoglobin, until October 2011. DCCT stands for Diabetes Control and Complications Trial. This means that the HbA1c values used in the original DCCT trial (ie measured in %) were used as standard values in the UK until recently.

Since then a new standard has been introduced - a more specific HbA1c value, expressed in mmol/mol. It’s prepared by an international organisation so allows global comparison of HbA1c results. This can be useful if abroad at the time of diagnosis and then you return to the UK.

But the new standard can often cause confusion so a chart has been created to help.

The table below will help you to identify your results and what they mean. It’s been taken from the guidelines written in September 2011 by the Macleod Diabetes and Endocrine Centre at the Royal Devon and Exeter Hospital.

Click on each result below and learn what your reading means.


HbA1c (%) HbA1c(mmol/mol)
 5.0  31
 6.0  42
 6.5  48
 7.0  53
 7.5  58
 8.0  64
 9.0  75
 10.0  86
 11.0  97
 12.0  108


What’s the difference between the HbA1c reading and the blood glucose reading from a finger prick test performed at home?

When you test your blood at home, the blood glucose monitoring device gives a measure of the concentration of glucose in your blood at that particular point in time only. Whilst this reading can be useful to indicate high or low blood glucose it doesn’t provide an overall or a long term measure like the HbA1c readings.

Blood glucose levels fluctuate constantly and differ from one minute to the next. This is the reason why your doctor or your diabetes nurse specialist may ask you to measure it at home at certain time of the day. For instance before meals, two hours after meals and possibly more frequently when you’re unwell. If, at those times, the levels are higher or lower than your usual readings the dose of insulin or certain tablets can be adjusted for those few times only. But you should discuss this at your consultation with your doctor or nurse before doing so.

Please note that not all patients with type 2 diabetes may be advised to check their blood glucose levels using finger pricking devices. Many such patients have their management adjusted based on HbA1c readings.

Consistently high or low HbA1c readings can let your doctor know whether they need to change your medication dosage or the diabetes medication itself.