Haemoglobin A1c (revision 3)
Old revision·06:51, 19 Aug 2024·SerialCommaSeb
| Haemoglobin A1c | |
|---|---|
| Abbreviation | HbA1c |
| Reflects | Average glucose over ~8–12 weeks |
| Units | mmol/mol (IFCC); % (DCCT/NGSP) |
| Confounded by | Anything altering red-cell lifespan |
| Topic infobox · conventions | |
Haemoglobin A1c is the fraction of haemoglobin that has been non-enzymatically glycated. Because glycation is irreversible and proceeds at a rate proportional to glucose concentration, the fraction integrates glucose exposure over the lifespan of the circulating red cells — roughly the preceding eight to twelve weeks, weighted towards the more recent.[1]
It is reported in two unit systems: mmol/mol under the IFCC reference method, and percentage under the older DCCT-aligned convention. Both appear in the literature and conversion between them is defined.[2]
What it measures
[edit]Glycation is a slow non-enzymatic reaction between glucose and the N-terminal valine of the haemoglobin β-chain. Its extent depends on both glucose concentration and exposure time, and because red cells are replaced continuously the population of cells sampled at any moment carries a weighted history.[2]
The weighting is not uniform: roughly half the value reflects the preceding month, and the remainder the two months before. A change made three weeks ago is therefore only partly expressed.[1]