The short version
- HbA1c reflects average blood glucose over roughly the previous three months
- Targets are individual — age, other conditions and hypo risk all change them
- A single reading matters less than the direction it is moving
- Some conditions make HbA1c unreliable, and your GP will use other tests instead
What it actually measures
Glucose in the blood attaches to haemoglobin in red cells. Because red cells live about three months, measuring how much haemoglobin is coated gives you an average of blood glucose over that period.
That is why it is used to track control over time. A finger-prick reading tells you about that moment; HbA1c tells you about the season.
Reading the number
HbA1c is reported in Australia as a percentage and in mmol/mol. Broadly, below 6.0% is the non-diabetic range, 6.0–6.4% suggests increased risk, and 6.5% or above on two occasions supports a diagnosis of diabetes.
For people already diagnosed, a target around 7% is common — but “common” is not “yours”. A younger person recently diagnosed with few other conditions may aim lower. An 85-year-old with heart disease and a history of hypos may have a higher target set deliberately, because the harm from low blood sugar outweighs the benefit of a tighter number.
When HbA1c is misleading
Because it depends on red cells, anything affecting them affects the result. Iron deficiency, recent blood loss or transfusion, some anaemias, pregnancy, kidney disease and certain haemoglobin variants can all distort it in either direction.
In those situations your GP will rely more on glucose readings, continuous glucose monitoring data or other measures. If your HbA1c does not match how you are actually tracking, say so — it is useful information.
What moves it
Food patterns — particularly the quantity and type of carbohydrate — physical activity, weight, sleep, stress, other illness, and medication. Activity works quickly: muscles take up glucose during and after exercise, independently of insulin.
A dietitian is the most commonly used allied health referral in diabetes for good reason. Under a care plan, Medicare subsidises up to five allied health visits a year — see care plan reviews.
The number is not a school report
People routinely arrive braced for a telling-off. Diabetes changes over time, and needing more treatment is the natural history of the condition rather than a personal failing.
If you have stopped testing, stopped coming in, or feel you are failing at it, that is worth saying out loud at your next appointment. It is extremely common, and it is usually the start of getting back on top of things. See diabetes care.
Common questions
Targets are individual. Around 7% is common for people with diabetes, but your target depends on your age, how long you have had diabetes, other conditions and your risk of hypos.
Usually every three to six months, more often when treatment is changing or control is unstable.
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