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The HbA1c is a blood test used to diagnose type 2 diabetes and assess how well your glucose has been controlled over the previous few months. Even though you may have had some very high or very low blood glucose levels, HbA1c will give you a picture of the average amount of glucose in your blood over that period. The result can help you and your doctor know if the measures you are taking to control your diabetes are working.

What is being tested?

As glucose circulates in your blood, some of it spontaneously binds to haemoglobin (the protein that carries oxygen in your red blood cells). This combination is called haemoglobin A1c (HbA1c). The amount of HbA1c formed is directly related to the amount of glucose in your blood. If your diabetes is not well controlled, your blood glucose levels are high, causing higher HbA1c levels. HbA1c levels do not change quickly since red blood cells live for 3-4 months. Because of this, the amount of HbA1c in your blood reflects the average amount of glucose in your blood during the last 2-3 months. The higher the level of glucose in the blood, the more glycated haemoglobin is formed.

 

How is it used?

The test for HbA1c can be used to diagnose diabetes and also indicates how well your diabetes has been controlled over the last few months. Even though you may have some very high or very low blood glucose values, HbA1c will give you a picture of the average amount of glucose in your blood over that time period. The result can help you and your doctor know if the measures you are taking to control your diabetes are working.

When is it requested?

When your doctor suspects that you might have diabetes. After diabetes has been diagnosed Diabetes Australia recommends that for all individuals HbA1c is measured every 3-6 months. HbA1c may be measured more frequently in those who have just been diagnosed with diabetes, in those whose blood glucose remains too high, or when a treatment plan changes.

What does the result mean?

Diagnosis of Diabetes  - HbA1c greater than or equal to 6.5% (48 mmol/mol)

Treatment targets:

  • General target <7% (53 mmol/mol) - If you have diabetes and your HbA1c is below the target of 7% (also reported as 53 mmol/mol) it is likely that your diabetes is in good control. If your HbA1c rises above 7% (53 mmol/mol), you are at increased risk of developing long term complications such as eye disease, kidney disease or nerve damage and probably heart attack and stroke.
  • Recurrent severe hypoglycaemia or hypoglycaemia unawareness  less than or equal to 64 mmol/mol, less than or equal to 8.0%=

Prediabetes - 42–47 mmol/mol (6.0–6.4%) Even though Labelling people with an HbA1c value slightly under 48 mmol/mol (6.5%) with prediabetes is not recommended, the levels suggest a higher risk of developing diabetes.

Is there anything else I should know?

  • Abnormal type of haemoglobin, for example if you suffer from sickle cell disease - accurate results will depend on the method used to measure your HbA1c.
  • Anaemia, excess breakdown of red blood cells (haemolysis) or heavy bleeding - test results may be falsely low.
  • Pregnancy can also affect the test result.
  • Iron deficiency, recent blood transfusion and erythropoietin therapy may affect your HbA1c measurement.

Common questions

  • Is there a home test for HbA1c?

Yes. HbA1c can be measured at home but it is not commonly done and can be expensive.

  • Can the HbA1c test be used to tell whether I have diabetes or not?

In the past, HbA1c testing was only subsidised for monitoring blood glucose control in patients with established diabetes. A new Medicare item now permits the HbA1c test to be used for diagnosing diabetes. The new MBS item allows the test to be done once per patient per year, with an HbA1c of greater than or equal to 6.5% (48mmol/mol) required for a diagnosis.

Using the HbA1c test is much simpler for patients than the fasting glucose test or the OGTT. This is because the test does not require fasting and can be done at any time of day.

The new test will not be suitable for a small number of patients with other illnesses including severe kidney and liver disease and certain blood disorders.

  • Why are there two results for HbA1c?

HbA1c is now usually reported with two sets of units. These are the % (NGSP) units with one decimal place which have been used for some time and the new Systeme International (SI) units which are mmol/mol with no decimal place and introduced into Australia in 2011. The new units relate to a revised international standard for HbA1c which was developed by the International Federation of Clinical Chemistry (IFCC) and therefore are sometimes known as IFCC units. To convert results in % units to SI units the following equation may be used: HbA1c (mmol/mol) = 10.93 x HbA1c (% units) – 23.5

More information

RCPA Manual: HbA1c

Last Updated: Thursday, 1st June 2023

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