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.
Due to the fact that red blood cells survive for 8-12 weeks before renewal, by measuring the HbA1C it can tell you how high your blood glucose has been on average over the last 8-12 weeks. The HbA1C test is currently one of the best ways to check diabetes and your control over blood sugar.
A normal non-diabetic HbA1C is 3.5-5.5%.
For non-diabetics, the usual reading is 4-5.9%.
For people with diabetes, an HbA1c level of 6.5% is considered good control, although some people may prefer their numbers to be closer to that of non-diabetics.
People at greater risk of hypoglycemia may be given a target HbA1c of 7.5%
But if the last reading is above 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. There are some studies and attempts being done to predict secondary complications in eyes, kidneys on the basis of HbA1c but these are in initial stages. Although HbA1c level alone does not predict diabetes complications, good control is known to lower the risk of complications.
Glucose levels fluctuate from minute to minute, hour to hour, and day to day. 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. 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.
One of the things happening today is that the HbA1c test is actually being used to diagnose diabetes. It has been for a long time but the fact is that people do a one off test. If your doctor does a one-off test on you, you might actually be at that stage of having a normal or low blood sugar, so you won’t show as having an abnormal blood sugar reading.
But if you have blood tests done over the space of a couple of weeks you might find that there are peaks and troughs that are not normal. Normal non diabetics simply don’t go out of this range, if the range is like this people stay within it. Diabetics tend to do this. You go over and above the norm. The HbA1c test is a stake in the ground, it’s literally something you can hang your hat on. You can’t judge all your diabetic control from it because of the fact that it’s average. If your HbA1c is 6.5% it might actually be hiding quite badly controlled diabetes, so you might be spending an awful lot of time having hypos which wouldn’t be very desirable in terms of quality of life.
Having said that it is very important because it’s the clearest indicator we have as to your long term ability to control diabetes.