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The past decade has given us a better insight into the clinical uses and problems associated with glycated haemoglobin measurement. This article describes the recent studies that have helped clarify the role of glycated haemoglobin in the management of patients with diabetes.
There remain numerous analytical problems associated with glycated haemoglobin measurement, such as the lack of assay standardisation and the problems related to its measurement in particular patient groups with haemoglobinopathies, fetal haemoglobin, renal failure (who form haemoglobin derivatives), and haemolytic diseases. These analytical problems have been reviewed recently1 and are not discussed at length here.
The term “glycated haemoglobin” is a generic one, which includes haemoglobin A1 (HbA1), HbA1c and “total glycated haemoglobin”. In recent years, improved analytical techniques have resulted in HbA1c measurement supplanting HbA1, to become the predominant measure of glycated haemoglobin, and all major clinical studies have used this assay. Therefore, I will concentrate on the HbA1c or HbA1c equivalent assays that are in routine use.
What is HbA1c?
Carbohydrates (such as glucose) can bind non-enzymatically to proteins (such as haemoglobin) in a process known as glycation. The charge separated haemoglobins of normal adult HbA0 are jointly known as HbA1, which can be further separated into its constituent parts, HbA1a1, HbA1a2, HbA1b, and HbA1c. Glucose is the carbohydrate in the major fraction, HbA1c, whereas other carbohydrates, some of which still need to be established with certainty, constitute the other fractions.2 The predominant glycated haemoglobin, called HbA1c, was first identified as a minor fraction of normal adult haemoglobin by ion exchange chromatography nearly four decades ago.3 Early structural studies suggested this HbA1c fraction exhibited glycation at the N-terminal valine of the haemoglobin …