Change to reporting of HbA1c – what is happening and why

From Monday 03 August , the way in which HbA1c results are reported in New Zealand is changing. The following explains why and how this will happen.

What is HbA1c ?

Glucose in the blood sticks to haemoglobin in red blood cells, making glycated haemoglobin, which is also known as haemoglobin A1c or HbA1c . The more glucose in your blood, the more HbA1c will be present, so the level reported will be higher.

What does it tell us?

Blood glucose levels can vary significantly throughout a day, and from day to day, but the HbA1c test tells us something different. Because red blood cells survive for 2-3 months before being replaced, the HbA1c test gives an indication of what the average blood glucose levels have been over a 2-3 month period.

Why measure it?

The closer your average blood glucose levels are to normal the lower is the risk of developing diabetes complications such as eye, kidney or nerve damage, heart disease or stroke. HbA1c (which is usually measured every 3-6 months) is the best measure we have for assessing long-term glucose control. It also helps us know if alterations in your diet, physical activity or medication have changed blood glucose control.

What are the current HbA1c results and targets?

The HbA1c results are currently given as a percentage. For most people with diabetes, the current HbA1c target is below 7.0%. However, you should have agreed your own individual target with your health care team, as sometimes a different target is more appropriate. For example, if you have had a lot of problems with low blood glucose levels (hypos), a higher HbA1c target might be safer.

What is changing?

Laboratories in New Zealand are about to change the way in which the HbA1c results are reported. The International Federation of Clinical Chemistry (IFCC) has put forward a new reference measurement method after discussion with diabetes groups worldwide. This will make it much easier to compare HbA1c results from different laboratories and from research trials throughout the world.

What are the new HbA1c results?

The way the results will be given is different from the old results, but the test still gives the same basic information about what your glucose control has been over the last 2-3 months. The measurement will be in millimoles per mole (mmol/mol) instead of percentage (%). Here is how the new results compare:

 

Current DCCT aligned units [ %]

New units [mmol/mol]

6.0

42

6.5

48

7.0

53

7.5

59

8.0

64

9.0

75

10.0

86

How will the targets change?

The equivalent of the current HbA1c target of 7.0 % is a new HbA1c target of 53 mmol/mol . (see the table above).

When will this happen?

The new units for HbA1c are obviously different from those currently in use. Everyone will need time to become familiar with the new units, and how they compare with the current result. So from 3 August 2009, all HbA1c results in New Zealand will be given as both the current HbA1c % and the new HbA1c units, mmol/mol.

So for example, the report of your HbA1c result might read:

Old HbA1c 6.9% New HbA1c 51 mmol/mol

The fact that the number is higher does not mean there is more glucose in your blood. It is just a different way of expressing the same thing.

When is the changeover to only new units?

This dual reporting will continue for a period of two years after which time it is envisaged that only the new, molar units will be reported.

The change is in response to the Position Statement issued by the New Zealand Society for the Study of Diabetes (NZSSD)
http://www.nzssd.org.nz/position_statements/standardisation.html