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DIABETES
How the A1c test worksHaemoglobin, found inside red blood cells, carries oxygen from the lungs to all the cells of the body. Like all proteins, haemoglobin links up with sugars such as glucose over time to form a glycated molecule. Most of these glycated haemoglobin molecules are referred to as A1C. A1C, therefore, is a fraction of the total amount of haemoglobin present. When you have poorly controlled diabetes you have too much sugar in your bloodstream. This extra glucose enters your red blood cells and links up (or glycates) with more molecules of haemoglobin than normal. The more excess glucose in your blood, the more haemoglobin gets glycated. By measuring the percentage of A1C in the blood you can get an overview of your average blood glucose control for the past few months. Suppose your blood sugar was high last week. During that time more glucose hooked up (glycated) with your haemoglobin. This week, your blood glucose is back under control. Still, your red blood cells carry the 'memory' of last week's high blood glucose in the form of more A1C. This record changes as old red blood cells in your body die and new red blood cells (with fresh haemoglobin) replace them. The amount of A1C in your blood reflects blood sugar control for the past 120 days, or the lifespan of a red blood cell. In people without diabetes, about 5% of all haemoglobin is glycated. For someone with diabetes and high blood glucose levels, the A1C level will be higher. How high depends on what the average blood glucose level was during the past weeks and months. Levels can range from normal to as high as 25% if diabetes is badly out of control for a long time. The importance of this test was underlined by two very large clinical trials in the US and UK which showed that A1C levels could predict the risk of long term complications such as heart and kidney disease or blindness. If you are diabetic you should have had your A1C level measured when your diabetes was diagnosed or when treatment for diabetes was started. To watch your overall glucose control, your doctor should measure your A1C level at least twice a year but if you change your diabetes treatment, such as start a new medicine, or if you are not meeting your blood glucose goals it should be about every 3 months. |