What is the HbA1c in Diabetes?

The HbA1c in diabetes is the most common term you will hear in the management and control of diabetes. Also known as glycated haemoglobin or A1c. The HbA1c is not the average glucose but reflects the average glucose for the previous 90 days.

Why is the HbA1c in Diabetes Important?

Everybody, including those without diabetes, has an HbA1c (usually less than 6%). The HbA1c develops when haemoglobin, a protein within red blood cells that carries oxygen throughout your body, after being exposed to glucose in the blood, joins with this glucose becoming ‘glycated’. From this you can see that the more glucose in the blood the more glycated haemoglobin, hence the more HbA1c that is measured.

The HbA1c in diabetes (the amount of haemoglobin that is glycated) is usually expressed as a percentage of the total haemoglobin (1). New measures report the A1c as a single number (mmol per mol) (2). For example, a HbA1c of 7%, is reported also as 53 mmol per mol and tells us that the average blood glucose level (BGL) is 8.6 mmol with a range of 6.8 to 10.3. See Table 1.

By measuring this HbA1c, doctors are able to get an overall picture of what the average blood glucose (some will use the term sugar) levels have been over a period of 90 days. It is well documented that the higher the HbA1c, the greater the risk of developing diabetes-related complications. For people with diabetes this is important.

The HbA1C assay is accepted as the most reliable means of assessing blood glucose control (3–5). Many studies have established the association between risk for long-term complications and high HbA1c. These same studies have shown that even a 0.9% reduction in HbA1c is rewarded with 20-40% reduction in complications (6-8). This reduced complication rate has led to the establishment of specific A1C targets for well controlled diabetes with the goal of preventing or delaying the development of long-term complications such as eye disease and vision loss, strokes, heart attacks, kidney disease, neuropathy and amputations (3, 9 –11).

Well controlled diabetes is associated with low risk of complication and events and is associated with good health, energy, vibrancy and well-being. Poorly controlled diabetes is associated with increased risk for events (we call these complications) reduced energy, poorer outcomes, less well-being.

The HbA1c in diabetes is the indicator of control and it can reflect quality of life. Some people have called it a quality of life number. The lower the A1c, the lower your risk of complications. The higher your A1c, the higher your risk of complications (6-8).

How does HbA1c Translate to Average Blood Glucose?

First, there is a very predictable relationship between HbA1c and average glucose. Understanding this relationship can help people with diabetes and their diabetes team set day-to-day targets for average glucose based on HbA1c goals. Second, the A1c Derived Average Glucose (ADAG) study has allowed mathematical conversion of HbA1c to an estimated average glucose and also conversion of average glucose to an estimated or predicted HbA1c. In this manner, when a person with diabetes does self-monitoring by testing their blood glucose for a few days, the average can be used to predict a HbA1c.

Further, this average can be used to check concordance with the blood sample HbA1c done at the pathologist. When there is no concordance, further discussion between the doctor and patient must take place to find an explanation.

Thirdly, fasting glucose should be used with caution as a surrogate measure of the average blood glucose because post meal increases are not captured on the fasting measurement but are reflected in the HbA1c.

Post meal (or postprandial) blood glucose is the predominant contributor to HbA1c in people satisfactory to good control of diabetes, whereas the contribution of fasting blood glucose increases with worsening diabetes. Post meal thresholds for predicting good or satisfactory control of diabetes are dependent on the timing of the meals (12).

Table 1: Estimated Average Glucose (13-14)

What is the Target HbA1c to Live with Well Controlled Diabetes?

If you have diabetes, the recommended HbA1c is less than 7%, and a tighter goal of 6.5% may be appropriate for some people (e.g. newly diagnosed and very young). These thresholds are further individualised according to age, duration of diabetes, life expectancy, complications (15).

So, what should your target be? International studies have concluded that age and presence of end organ damage are factors we should consider when determining personal targets (16). The Australian Diabetes Society also takes into consideration duration of diabetes, medications and hypoglycaemia events.


Conclusion: Understanding HbA1c in Diabetes

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