What is the HbA1C?

David Kinshuck


Enlarge  Haemoglobin, in your blood, joins up with glucose to form the chemical called HbA1c


In the blood stream the red blood cells are made of a molecule, haemoglobin. The glucose in the blood sticks to this haemoglobin to make 'glycosylated haemoglobin' . This is called haemoglobin A1C or HbA1C.

The more glucose in the blood, the more haemoglobin A1C or HbA1C will be present in the blood.

Red cells live for 8 - 12 weeks before they are replaced. By measuring the HbA1C it can tell you how high your blood glucose has been on average over the last 8-12 weeks. A normal non-diabetic HbA1C is <36mmol/mol  (5.5%). In diabetes about 48mmol/mol  (6.5%) is good.

The HbA1C test is currently one of the best ways to check diabetes is under control; it is the blood test that gets sent to the laboratory, and it is done on the spot in some hospital clinics. Remember, the HbA1C is not the same as the glucose level.

In practice GLUCOSE levels that average 6.5 before meals are equivalent to HbA1C 60mmol/mol (7%).


Two examples

Below are two examples of people who have their HbA1c measured. One is poorly controlled, one well controlled.

A graph of glucose changes over 9 weeks. The glucose (green line) changes between 7-12.

This results in an HbA1c level of 86mmol/mol  (10%) at the end of the 9 weeks (red line). Poorly controlled.

Here the glucose changes between 5-9.

This results in an HbA1c level of 53mmol/mol (7%) at the end of the 9 weeks. Well controlled.







When should the HbA1C be measured?

Measure HbA1c
  • every 3 months if trying to improve
  • every 6 months if very stable



If your diabetes is controlled (basically an HbA1C lower than 53mmol/mol  ( 7% ), every 3-6 months.

But if the last reading is above 53mmol/mol  (7%) and you are in reasonable health, you will need to achieve a lower level if possible, and the next reading should be sooner. This assumes you will make changes to improve your control. There is no point in having your HbA1c measured if you are not trying to achieve good control of your diabetes, although the level does predict the likelihood of complications from your diabetes.

Your ideal HbA1c depends on your general health, and whether or not you use insulin, etc, and is discussed here.

For insulin users, if Hba1c > 100 , it suggests the patient is missing out the insulin.


Illustrated diagrammatically

Haemoglobin in the blood (red, rectangle) combines with glucose in the blood (green, circle) to form glycosylated haemoglobin. This reaction occurs over a 10 week period.


Controlled diabetes, not much glucose, not much glycosylated haemoglobin


Uncontrolled diabetes, more glucose, much more glycosylated haemoglobin.


Glucose levels fluctuate from minute to minute, hour to hour, and day to day. Thus for hour to hour control, or day to day, a glucose level is the best guide.
The HbA1C level changes slowly, over 10 weeks, so it can be used as a 'quality control' test.
In diabetes glucose tend to rise more than usual, dropping with exercise, rising after food, rising a lot more after sweet food, and can make it hard to control.

For how to lower the HbA1C to achieve better control (and better health in the long term), see the pages type 1 diabetes/insulin (type2) or type 2 diabetes (no insulin).   Good control produces benefits that lasts 10 years at least (NEJM 2008).


Comparing glucose level with HbA1c, new/old units


IFCC-HbA1c  mmol/mol HbA1c % Average blood glucose level mmol/l
120 13 18
108 12 16.5
96 11 15
86 10 13
75 9 12
69 8.5 11
64 8 10
58 7.5 9.4
53 7 8.6
48 6.5 7.8
42 6 7.0
31 5 5.4



Diagnosing diabetes

Diabetes may be defined as having an HbA1c > 48mmol/mol (6.5%) (Pulse 2010). So,

Duration of diabetes

Type 2 diabetes may be present for many years before it is diagnosed. Blood pressure levels and proteinuria may be proxy measurement for the length of time diabetes has been present...the higher the blood pressure and the greater the proteinuria, then the longer time diabetes has been present.

This combination of blood pressure levels and proteinuria may also be used to determine how long a type 1 diabetic has had poor control.


HbA1c inaccuracies

BMJ 18 The HbA1c is less accurate BMJ 18