Change in HbA1c Reporting
From 1st June 2009 the HbA1c test will be changing from a percentage figure to a measurement in mmol/mol. To make the transition easier the new measurement will appear alongside the old measurement until 31st May 2011. What is HbA1c?The HbA1c is also known as Haemoglobin A1c or Glycated Haemoglobin test. It is based on how much glucose (sugar) binds to the red haemoglobin pigment in red blood cells forming A1c (HbA1c). The more glucose in the blood, the more glucose binds to the haemoglobin, resulting in a higher HbA1c. Research trials like the Diabetes Control and Complications Trial in type 1 diabetes (DCCT, 1993) and the UK Prospective Diabetes Study (UKPDS, 1998) in type 2 diabetes are both large studies showed that as the HbA1c increased so did the risk of developing long-term microvascular (kidneys, eyes and nerves) and macrovascular (heart, brain and major arteries) complications. These trials demonstrated the importance and benefits of long-term good blood glucose control in both type 1 and type 2 diabetes. Why measure the HbA1c?The HbA1c test measures the average blood glucose over the past two to three months, which is how long red blood cells live in the body. The HbA1c measurement is crucial in the management of diabetes as it means that it is possible to assess the individual's current blood glucose control, their risk of developing diabetes complications and the effectiveness of medication and lifestyle changes such as dietary, weight loss and exercise. What is the HbA1c Target?The general target for people with diabetes is below 6.5% but may be set at 7.5% for those at risk of severe hypoglycaemia (low blood glucose). The target should always be individualised according to the individual's circumstances and agreed with your supervising health care professional (Diabetes UK, 2009). The table shows how the current HbA1c result relates to an individual's average blood glucose level (Adapted from Nathan et al., (2008)): | Current HbA1c (%) | Average Blood Glucose (mmol/L) | | 6 | 7.0 | | 7 | 9.0 | | 8 | 10.0 | | 9 | 12.0 | | 10 | 13.0 |
Why change HbA1c reporting?The change in reporting will make it easier to compare results from different laboratories and studies from around the world. The new HbA1c reference is more accurate than the assays used up to now. It is important to know that the blood glucose target will not change and that it is simply a change in the way it will now be reported (mmol/mol not %). The current HbA1c target of 6.5% will become 48mmol/mol (Diabetes UK, 2009). The new higher figure does not mean there is more glucose in the blood and control or that diabetes control is worse. The table shows the current HbA1c and the new HbA1c level: | Current HbA1c (%) | New HbA1c (mmol/mol) | | 6.0 | 42 | | 7.0 | 53 | | 8.0 | 64 | | 9.0 | 75 | | 10.0 | 86 |
A useful equation to convert old (whole percentages) to the new figures is called "minus two minus two", for example if the old HbA1c is 9%, the new HbA1c is nine minus two (7) minus two (5) which is 75mmol/mol' (Kilpatrick, 2009). ReferencesDiabetes Control and Complications Trial (1993) The effects of intensive treatment of diabetes on the development and progression of long-term complications in insulin-dependent diabetes mellitus. New England Journal of Medicine 329, 977-986 Diabetes UK (2009) via website www.diabetes.org.uk Kilpatrick E.S (2008) Haemoglobin A1c in the diagnosis and monitoring of diabetes mellitus. Journal of Clinical Pathology 61, 977-982 Nathan D.M et al., (2008) Translating Glucose to A1c Assay Into Estimated Average Glucose Values. Diabetes Care 31, 1-6 U.K. Prospective Diabetes Study Group (UKPDS 33) (1998) Intensive blood glucose control with sulphonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes. Lancet 352, 837-853.
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