In the blood stream are the red blood cells, which are made of a molecule, haemoglobin. Glucose sticks to the haemoglobin to make a ‘glycosylated haemoglobin’ molecule, 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 3.5-5.5%.
Two major studies: The Diabetes Control and Complications Trial (DCCT USA) and the United Kingdom Prospective Diabetes Study (UKPDS) confirmed that intense blood sugar control can dramatically reduce the risk of long term diabetic complications. They discovered that those with an Hba1c of 7% could reduce the risk of retinopathy (eye disease) by 76% over those with an Hba1c of 9%. Similarly the risk of Nephropathy (kidney disease) reduced by 54% and neuropathy (nerve disease) by 60%. Every 1 point reduction in Hba1c corresponds with about a 30% reduction in your risk of developing complications. Reduce your Hba1c from 10 to 9 and you reduce the risk by 30%, reduce it from 9 to 8 and you reduce it by a further 30%. Therefore it behoves us to work towards getting the best Hba1c possible.
A word of caution here, in insulin dependant diabetics it is possible to have a great Hba1c e.g. 5% but if this is achieved by wild swings in BGs say from 20 down to 1.8 with frequent hypoglycaemic incidents (hypos) then you are not reducing your risk at all. This is unlikely to occur with T2s on oral meds.
So, if my Hba1c is great then I have no problems? Well not quite… you need to keep your BGs steady as much as possible, iron out those post-prandial spikes and work on your control every day and therefore you need to test regularly. The Drs who contend that it is enough to have a 3 monthly Hba1c to assess your control are wrong. In order to get that good Hba1c you need to be testing every day (several times a day) to see what different foods affect you and how. Otherwise you are working in the dark. You can find more information on blood glucose testing here and how to monitor how food affects you here.
Relationship between Hba1c and average blood glucose (BG)
HbA1c – Converting mmol/mol results to %
Now that clinics and surgeries have switched over to the providing HbA1c results in IFCC ‘mmol/mol’ units you might be finding it tricky to get a feel for the new units and wonder what your result would have been expressed as a percentage.
Here’s a table of conversions that you can use as a ready reckoner:
If you’d like to calculate your own % result exactly you can use this formula:
From mmol/mol to %
From % to mmol/mol
Alternatively you can use the online calculator on the Diabetes UK website.