HbA1c
What is HbA1c?
Within the circulation sugars can bind non enzymically to haemoglobin. Binding of glucose to the N terminal valine of the beta chains of HbA (the normal adult haemoglobin) forms a glycated haemoglobin called HbA1c. Normally about 4-6% of the circulating haemoglobin is in this form.
The lifespan of a red blood cell is about 12 weeks. Assuming normal red cell lifespan, HbA1c thus reflects the average plasma glucose concentration over the preceding 12 weeks.
Other sugars may also bind to haemoglobin to give other forms of haemoglobin
Why measure HbA1c?
Studies have shown that in both Type 1 diabetics (Diabetes Control and Complications Trial - DCCT) and Type 2 diabetics (UK Prospective Diabetes Study - UKPDS) that the better the control of blood glucose over time, as assessed by HbA1c, then the fewer longterm complications from diabetes will occur.
How is HbA1c measured?
A fluoride oxalate whole blood (yellow top) or EDTA whole blood (red top bottle) sample is required (paediatric samples are collected into HbA1c capillary collection tubes).
There are several methods available to determine HbA1c. The method used at Barnsley -Rotherham uses ion exchange chromatography.
What do the results mean?
In the past HbA1c was reported as a percentage with a normal range of 4 - 6% (DCCT System). As a result of international standardisation (IFCC) of the HbA1c method the HbA1c results are now reported in mmol/mol such that the normal range is 20 - 42 mmol/mol. The relationship between the two units is given by
DCCT value (%) = 0.0915 x IFCC value (mmol/mol) + 2.15
Web based converters are also available to convert between the 2 values
See Diabetes.co.uk site and Diabetes UK site for further information
Within the circulation sugars can bind non enzymically to haemoglobin. Binding of glucose to the N terminal valine of the beta chains of HbA (the normal adult haemoglobin) forms a glycated haemoglobin called HbA1c. Normally about 4-6% of the circulating haemoglobin is in this form.
The lifespan of a red blood cell is about 12 weeks. Assuming normal red cell lifespan, HbA1c thus reflects the average plasma glucose concentration over the preceding 12 weeks.
Other sugars may also bind to haemoglobin to give other forms of haemoglobin
Why measure HbA1c?
Studies have shown that in both Type 1 diabetics (Diabetes Control and Complications Trial - DCCT) and Type 2 diabetics (UK Prospective Diabetes Study - UKPDS) that the better the control of blood glucose over time, as assessed by HbA1c, then the fewer longterm complications from diabetes will occur.
How is HbA1c measured?
A fluoride oxalate whole blood (yellow top) or EDTA whole blood (red top bottle) sample is required (paediatric samples are collected into HbA1c capillary collection tubes).
There are several methods available to determine HbA1c. The method used at Barnsley -Rotherham uses ion exchange chromatography.
What do the results mean?
In the past HbA1c was reported as a percentage with a normal range of 4 - 6% (DCCT System). As a result of international standardisation (IFCC) of the HbA1c method the HbA1c results are now reported in mmol/mol such that the normal range is 20 - 42 mmol/mol. The relationship between the two units is given by
DCCT value (%) = 0.0915 x IFCC value (mmol/mol) + 2.15
Web based converters are also available to convert between the 2 values
See Diabetes.co.uk site and Diabetes UK site for further information
6.5% = 48 mmol/mol
7.0% = 53 mmol/mol
7.5% = 59 mmol/mol
8.0% = 64 mmol/mol
9.0% = 75 mmol/mol
7.0% = 53 mmol/mol
7.5% = 59 mmol/mol
8.0% = 64 mmol/mol
9.0% = 75 mmol/mol
