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HbA1c Explained

HbA1c Explained

What is HbA1c?

HbA1c is formed when haemoglobin (the molecule in red blood cells responsible for carrying oxygen and carbon dioxide) joins up with glucose.


Why is HbA1c Important?

It can be used to diagnose diabetes and it is a good indicator of your glucose control over the previous 2-4 months.

Blood glucose combines with haemoglobin to form HbA1c – so a persistently high blood glucose causes a high HbA1c …


Using HbA1c to Diagnose Diabetes

HbA1c can be used to diagnose diabetes …

HbA1c above 48 mmol/mol (or 6.5%) = diabetes.
HbA1c under 42 mmol/mol (or 6.0%) = not diabetic.
HbA1c between 42-48 mmol/mol (or 6.0-6.5%) is ‘pre-diabetes’ or ‘at high risk of diabetes’.

Using HbA1c to Monitor Diabetes

As shown above, HbA1c is an indication of your average blood sugar over the previous 2-4months.

*It is very important that your own target should be set by your GP or diabetic care team.
*People without diabetes should have an HbA1c of around 20-41 mmol/mol.
*Diabetics will have varying targets depending on their likelihood to experience low blood glucose.
*HbA1c used to be recorded as a percentage (e.g. 6.0%) – it is now recorded as a number (e.g. 42 mmol/mol).

Here is a conversion table …
6.0% = 42 mmol/mol
6.5% = 48 mmol/mol
7.0% = 53 mmol/mol
7.5% = 58 mmol/mol
8.0% = 64 mmol/mol
9.0% = 75 mmol/mol

There is a free convertor available on itunes – HbA1c Converter

Who Should Be Tested?

Undiagnosed? If you are not diabetic but are at high risk on our Self Assessment Tool or if you have symptoms of tiredness, thirst and passing urine frequently you should see your GP who may well decide to test your HbA1c.

Type 2 Diabetic? You should be tested every 3 months if you are trying to improve your blood glucose control, or every 6 months if your control is stable.

Type 1 Diabetic? HbA1c testing is not recommended for children or young people. It is also of no use if blood glucose levels are changing erratically which can be the case in Type 1. There is some evidence to suggest that HbA1c testing can be of benefit in helping to control glucose levels in some circumstances (NEJM 1990) but you should consult your GP or diabetic team for information relevant to your specific circumstance.

Gestational Diabetes? HbA1c testing is not recommended.

When Should HbA1c Levels NOT Be Used?

HbA1c levels are NOT recommended for …

Children / Young people
In gestational diabetes (i.e. pregnancy)
If you have a haemoglobinopathy
If you have iron deficiency anaemia
If you have had diabetes for less than 2 months

When Might HbA1c Levels Be Misleading?

Factors that influence the levels and function of haemoglobin and/or its interaction with glucose can cause misleading HbA1c results.

The test should therefore be interpreted with caution in the following circumstances …

Type 1 diabetes
Those who are acutely unwell
After acute pancreatic damage (pancreatitis, pancreatic surgery)
After a recent blood transfusion
Those with renal failure
Those with a haematological illness
Those taking steroids or antipsychotics

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