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GLYCATED HAEMOGLOBIN (HbA1c)

Definition

The body converts blood sugar into energy in the body by a hormone called insulin. However, people with diabetes do not produce sufficient insulin, therefore blood sugar is not converted into energy, which causes high blood sugar levels (glycemia).

In previous years, fasting plasma glucose has been the measurement of choice for diagnosing diabetes, however these levels fluctuate from day to day. Glycated haemoglobin (HbA1c) on the other hand has recently been endorsed by WHO as the measurement of choice for the diagnosis of diabetes.¹ HbA1c, in simple terms, is haemoglobin which is bound to a glucose particle in the blood for the average life span of a red blood cell (around 120 days). HbA1c levels generally reflect the average blood glucose over three months.

The HbA1c test measures the amount of glucose circulating in the blood that binds to the haemoglobin present in red blood cells, forming HbA1c. Mature red blood cells live for approximately three months within the blood circulation, which enables this test to measure chronic (long term) glycemia.

Population

HbA1c test results were obtained for persons aged 18 years and over, who agreed to participate in the National Aboriginal and Torres Strait Islander Health Measures Survey (NATSIHMS) and who provided a blood sample. Fasting was not required for this test.

Methodology

A blood sample was collected from participants and HbA1c (%) levels were measured at the Douglass Hanly Moir (DHM) laboratory.

In the NATSIHMS, cut off reference values for normal and abnormal results were sourced from the World Health Organization (WHO) guidelines¹ and the position statement for diagnosing diabetes in Australia.² These guidelines are based on epidemiological data and publications of major clinical trials.

HbA1c units of measurement were reported in the NATSIHMS using both the National Glycohemoglobin Standardization Program (NGSP) units (percentage) and the Système International (SI) units (mmol/mol) as recommended by the International HbA1c Consensus Committee.³ In the NATSIHMS, the following equation was used to convert the HbA1c units of measurement from percentage to mmol/mol, as described in the Diabetes Australia guidelines.⁴

	HbA1c levels (%)	HbA1c levels (mmol/mol)
Has diabetes (Abnormal)	≥6.5	≥48
At high risk of diabetes	6.0 to <6.5	42 to <48
No diabetes (Normal)	<6.0	<42

• It should be noted that the HbA1c results, on their own, do not satisfy the definition of diabetes in the NATSIHMS. Information about the definitions for measuring diabetes is available from the Diabetes biomarkers topic page of this chapter.
• HbA1c test results do not confirm a specific diagnosis without consultation with a health professional.
• Where HbA1c levels indicate a person is at risk of diabetes, prevention interventions might be considered such as lifestyle modifications to achieve HbA1c targets.²
• The NATSIHMS cut off reference ranges are based on measuring chronic glycemia periodically and this test may be repeated every 3 or 6 months depending on HbA1c levels and upon consultation with a health professional.
• HbA1c levels are affected by conditions that affect red blood cell survival time or non-enzymatic glycation of haemoglobin.²
• There are a number of different test methods for measuring HbA1c, which may produce different results. The data from this topic should therefore be used with caution when comparing HbA1c results from other studies using a different test method or equation.