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
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 level during that period.
Studies have shown that there’s an association between the HbA1c readings and the person’s risk of developing complications from diabetes.
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 a percentage of haemoglobin, until October 2011. DCCT stands for Diabetes Control and Complications Trial. This means that the HbA1c values used in the original DCCT trial (i.e. measured in percentages) 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.
If you're more comfortable with the percentage system, Diabetes UK have a conversion tool that can help.
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. While 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 or desired readings, the dose of insulin or certain tablets can be adjusted to maintain normal sugar levels in your blood. This is usually done in consultation with your nurse or doctor.
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.
Further support and information
Visit AXA Health's diabetes health centre for more information and tips to help managing your condition. Or, if you have a specific question about diabetes or any aspect of your or your family's health, we're here to help at any time of the day or night. Simply submit your query online though our Ask the Expert service and one of our team will get back to you.