Makindo Medical Notes

Related Subjects: Type 1 DM |Type 2 DM |Diabetes in Pregnancy |HbA1c |Diabetic Ketoacidosis (DKA) Adults |Hyperglycaemic Hyperosmolar State (HHS) |Diabetic Nephropathy |Diabetic Retinopathy |Diabetic Neuropathy |

The HbA1c is an important reflection of glucose control over a 3 month period (life expectancy of the erythrocyte).

About

• Gives some guidance as to long term glucose levels which otherwise change significantly over a day
• There is a good relationship between the glucose level and its ability to glycosylate the Hb molecule
• HbA1c concentration reflects the integrated blood glucose control over the lifespan of erythrocytes (120 days),
• HbA1c is sensitive to changes in glycaemic control in 4 weeks prior to measurement.
• HbA1c values are now reported in mmol/mol and IFCC HbA1c (mmol/mol) = [DCCT HbA1c(%)-2.15] × 10.929
• 11 mmol/mol in HbA1c corresponds to an approximate average increase of 2 mmol/L (36 mg/dL) in blood glucose

Aetiology

• 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 six weeks.
• Fructosamine is a glycosylated protein, usually albumin. Indicates control over 2-3 weeks.

Uses

• A HbA1c > 8% requires is best managed with pharmacotherapy rather than diet alone and HbA1c > 9% is best considered for Insulin
• 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%
• 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) HbA1c 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.
• 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%