HBA1c explained

Haemoglobin A1c; glycated haemoglobin; glycosylated haemoglobin

To diagnose diabetes, to monitor a person’s diabetes and to aid in treatment decisions

When first diagnosed with diabetes and every 3-6 months

A blood sample drawn from a vein in the arm or from a fingerstick

None

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 few months.

Your blood may be drawn from a vein in your arm or, in some cases, a drop of blood from a finger-prick may be used.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

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 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.

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.

If you have an 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. If you suffer from a condition causing excess breakdown of red blood cells (haemolysis) or heavy bleeding, your test results may be falsely low. Pregnancy can also affect the test result. Finally, if you are iron deficient or have recently been treated for iron deficiency, this may affect your HbA1c measurement.

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

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 ≥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.

HbA1c is now usually reported with two sets of units. These are the % units which have been used for some time and the new Systeme International (SI) units which are mmol/mol. 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