What is HbA1c testing?
The HbA1c test (also called glycosylated haemoglobin level) is a laboratory blood test which measures your average blood glucose over the previous weeks and gives an indication of your longer-term blood glucose control. The test is used as a regular monitoring tool if you have been diagnosed with diabetes. It may also be used as one of several screening measures in the general population to look for elevated blood glucose levels, which are suggestive of diabetes.
How useful is the test?
Most diabetes specialists and GPs have a lot of confidence in this test and will use it to help show people with type 1 or type 2 diabetes how they are going with their blood glucose management. The HbA1c measures how much glucose has become stuck onto your red blood cells. Red blood cells have a lifespan of about six weeks and so the test gives a good indication of what your overall blood glucose levels have been throughout that time.
The HbA1c level is not directly equivalent to blood glucose levels. For example, an HbA1c level of 13% means that your average blood glucose level for the past six weeks has been around 18-19 mmol/L.
Change to reporting values from October 2011
HbA1c levels have previously been measured as a percentage (%). However, from October 2011, New Zealand laboratories will be reporting HbA1c values in IFCC (International Federation of Clinical Chemistry and Laboratory Medicine) format, which is in mmol/mol.
What are healthy HbA1c levels?
Target HbA1c levels will vary from person to person. Work out a safe target HbA1c for you with your doctor.
A general range for HbA1c levels [equivalent IFCC values in square brackets] is:
- Less than or equal to 7% [up to 53mmol/mol] is a very healthy HbA1c level
- Between 7% and 8% [54 - 64mmol/mol] is a fair HbA1c level and needs work to improve
- Between 8% and 10% [65 - 86mmol/mol] indicates your blood glucose levels are much too high
- Above 10% [87mmol/mol or higher] indicates your blood glucose levels are extremely high.
Note: If you are taking insulin and your HbA1c level is less than 6.2% [44mmol/mol] this almost certainly indicates that you are having lots of low blood glucose levels ('hypos' or hypoglycaemia). Having HbA1c levels this low is not safe when you are taking insulin.
Also see: Low blood glucose type 1 diabetes and Low blood glucose type 2 diabetes
How does lowering my high HbA1c level help me?
A major study, the UK Prospective Diabetes (UKPDS) Study* published in 2000, managed to quantify many of the benefits of reducing a high HbA1c level by just 1%.
- a 16% decrease in risk of heart failure
- a 14% decrease in risk of fatal or non-fatal myocardial infarction (heart attack)
- a 12% decrease in risk of fatal or non-fatal stroke
- a 21% decrease in risk of diabetes-related death
- a 14% decrease in risk of death from all causes
- a 43% decrease in risk of amputation
- a 37% decrease in risk of small blood vessel disease (eg, retinal blood vessel disease causing vision loss).
Getting your blood glucose and HbA1c levels down into the optimal ranges means working with your doctor or diabetes nurse on implementing a range of diet, weight control and lifestyle measures as well as learning to use medications that help to control the way your body uses glucose. Regular self-monitoring of blood glucose also helps you learn how to control your blood glucose level.
Also see: High blood glucose type 1 diabetes and High blood glucose type 2 diabetes
*Stratton IM, Adler AI, Neil HA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKDPS 35): prospective observational study. British Medical Journal 2000; 321 (7258): 405-12.
See also: Laboratory tests for diabetes
Original material provided by Diabetes New Zealand and everybody. Reviewed by everybody, August 2011.