2.5 HbA1c levels
Another way of assessing blood glucose control is by measuring the glycated haemoglobin. This test is abbreviated to HbA1c. Haemoglobin is a protein that is found in red blood cells and its function is to transport oxygen around the body. Red blood cells are functional for about 90 days, after which they are broken down in the spleen, along with the haemoglobin contained within them. Glucose reacts with protein over time, changing it (or ‘glycating’ it). By taking a sample of red cells and measuring how much of the haemoglobin within them has been changed by this process, the result gives an idea of what the blood glucose level has been like in the last two to three months for that person. If the blood glucose level has been high, a greater proportion of the haemoglobin will have been in contact with glucose and will have become glycated than if the blood glucose level has been normal or low. This is a process that occurs even in someone without diabetes, so there is a ‘normal’ range of glycated haemoglobin. The aim of diabetes treatment is to enable someone to control their blood glucose as well as possible so that their HbA1c result is similar to that of someone without diabetes. The result is measured as a percentage of total haemoglobin changed, and depending on the techniques used in your local laboratory, the normal result is usually less than 6.5 per cent. Guidance from NICE (the National Institute for Health and Clinical Excellence) recommends that most people with diabetes should aim for results of between 6.5 and 7.5 per cent or less (NICE, 2002). The GMS2 (General Medical Services) contract also encourages GPs to help at least 50 per cent of their patients to get this result. However, it is very difficult for most people to achieve, particularly if the risk of hypoglycaemia is too high. If you have diabetes, and are not able to achieve this target, you should be reassured that any reduction in HbA1c will reduce your risk of developing microvascular complications.
Activity 4 Finding out about HbA1c testing
Find out what is considered to be the normal range for HbA1c at your local diabetes clinic. If you have diabetes yourself, do you know what your last result was, and is it within the target range? Also, check how HbA1c is measured at the clinic.
HbA1c can be checked using a venous blood sample which is sent to the laboratory, or your diabetes clinic may use a machine that analyses a finger-prick capillary sample of blood, where the result is available within a few minutes.