Blood Glucose Levels and HbA1c
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“HbA1c” is a clinical measure that gives a good indication of your ‘diabetes health’ in terms of blood glucose levels over recent weeks.
HbA1c can also be used to diagnose diabetes and pre-diabetes [see Diagnosis of Diabetes].
Healthy Blood Glucose levels
Given that diabetes is defined as a higher blood glucose level it stands to reason that for a person with diabetes one of the keys to staying healthy is to keep blood glucose levels in a healthy range.
The aim of diabetes treatment is to keep blood glucose levels as close to ‘normal’ as possible without placing the person with diabetes at risk of hypoglycaemia.
So people with diabetes should aim for optimal blood glucose levels and this target range will be confirmed by your doctor or diabetes nurse.
Everyone is different; the numbers provided here are a guideline only, based on national and international guidelines.
| Blood Glucose Level | NZ units millimoles per litre (mmol/l) |
US units milligrams per decilitre (md/dl) |
| Healthy range a | 4.4 – 8.0 mmol/l | 80 – 144 mg/dl |
| On the low side b | 3.0 – 4.4 mmol/l | 54 – 79 mg/dl |
| Too low b
(Hypoglycaemic) |
< 3.0 mmol/l | < 54 mg/dl |
| Too high a
(Hyperglycaemic) |
> 8.0 mmol/l | > 144 mg/dl |
| a Depends on time of test in relation to last meal and time of day (see ‘Target ranges’ below) | ||
| b Significant hypoglycaemia is usually ‘defined’ as a blood glucose level less than 3.0 mmol/l – however in practise most people will suffer symptoms at levels higher than this. The general recommendation is to treat for any reading below 4.0 mmol/l. | ||
For more on Blood Glucose Monitoring visit:
What is HbA1c?
HbA1c is basically haemoglobin with glucose stuck to it. The level of HbA1c in the blood reflects blood glucose levels of the preceding 6-8 weeks.
HbA1c is a modified form of haemoglobin. Haemoglobin is the molecule in our red blood cells which carries oxygen around the body. Glucose molecules attach themselves to the haemoglobin. Over time, more and more glucose attaches to the haemoglobin at a rate that reflects the blood glucose levels. The process of glucose attaching to another molecule is called ‘glycosylation’ or ‘glycation’.
The amount of haemoglobin which forms HbA1c will depend on:
- The concentration of glucose that the haemoglobin is exposed to
Not all cell types in the body require insulin for the uptake of glucose. Red blood cells have ‘insulin-independent’ glucose transporters on their surface. So if glucose levels in the plasma (the watery part of the blood) are high, then glucose levels inside the red blood cells will also be high. The higher the blood glucose level, therefore, the more glycosylation of haemoglobin will occur.
- The length of time that the haemoglobin is exposed to a given concentration of glucose
The longer the blood glucose level is high, the more glycosylation will occur.
You can learn more about HbA1c from the page on Lab Tests.
Last updated: Jan 2025
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