glycosylated haemoglobin measurement
Last reviewed 07/2023
Glycosylated haemoglobin (Hb A1) measurement is the most widely used measure of longterm glycaemic control in diabetes.
Glycosylated haemoglobin is produced by the non-enzymatic glycosylation of haemoglobin at a rate proportional to the prevailing glucose concentration. The level of Hb A1 depends upon:
- red cell lifespan
- prevailing blood glucose concentration
Providing red cell lifespan is normal, Hb A1 measures mean blood glucose concentration over the preceding 60 days - i.e. half-life of red cell.
Some assays measure total glycosylated haemoglobin whilst others measure Hb A1c produced by glycosylation of the N-terminal valine of the B-chain of haemoglobin.
Notes:
- the HbA1c results will be reported exclusively as mmol/mol of haemoglobin without glucose attached, rather than a percentage as previously, from June 1st 2011
- the International Federation of Clinical Chemistry and Laboratory Medicine
(IFCC) has initiated the change:
- the equivalent of the current DCCT HbA1c targets of 6.5% and 7.5% are 48 mmol/mol and 59 mmol/mol in the new units, with the nondiabetic reference range of 4.0% to 6.0% being 20 mmol/mol to 42 mmol/mol
-
DCCT- HbA1c (%) IFCC-HbA1c (mmol/mol) 6.0 42 6.5 48 7.0 53 7.5 59 8.0 64 9.0 75
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