About
- Glycosylated haemoglobin is due to a covalent bond between glucose and a terminal valine of the beta chain of haemoglobin HbA.
- The percentage is the percentage of glycosylated Hb as a total of all Hb.
- The amount is proportional to glucose levels over about 6 weeks.
- Fructosamine is a glycosylated protein usually albumin. Indicates control over 2-3 weeks.
Interpretation
- HbA1c normal value in population is 4.5-6.5%
- Standardisation uses HbA1c equivalents to avoid inter-lab errors
- Type 1 diabetes (DCCT trial)
- Type 2 DM (UKPDS) HbAic was a marker of microangiopathy
- A HbA1c > 8% is best managed with pharmacotherapy rather than diet alone and HbA1c > 9% is best considered for Insulin.
- A HbA1c may be falsely low in those with haemoglobinopathies.
- Fructosamine is preferred for assessing glucose control in pregnancy as it has a shorter half-life and gives a more accurate account of recent blood glucose control.
- Fructosamine is also preferable with haemoglobinopathies such as thalassaemia and sickle cell.
- Target HbA1c is about 6.5-7.0% but this is often unobtainable and 7.0% is a more realistic target.
- On average oral anti-diabetic agents tend to lower HbA1c by about 1%