Analysis of HbA1c
How is HbA1c Measured?
The concentration of HbA1c is measured and expressed as a percentage of the total hemoglobin. The methods used to analyse HbA1c fall into one of three main types. These are:
- Ion Exchange HPLC
- Immuno Assay
- Glycation specific. This includes boronate affinity and chemical methods such as the thiobarbituric acid method.
- Enzymatic methods employing the enzyme frutosyl valine oxidase with a peroxide detection reaction.
The first two method types more specifically measure HbA1c. The third method measures the amount of glucose bound to hemoglobin and uses a conversion factor to derive the HbA1c level.
The best primary reference methods use electrospray ionisation mass spectrometry to accurately measure the ratio of the β chain N-terminal hexapeptide with the glucose attached to that without the glucose.
Why Measure HbA1c?
The measurement of HbA1c is especially useful in insulin-dependent diabetic patients where blood glucose levels fluctuate widely and where the instantaneous blood glucose does not reflect the averaged situation. The formation of HbA1c occurs slowly (about 0.05%/day) and continuously during the 120-day lifetime of the red cell. Hence the measurement of HbA1c is useful to physicians as a long-term integral of blood glucose concentration and thus as a measure of the degree of control or self-management by the diabetic patient. The normal range for HbA1c is 4% – 6% of total hemoglobin. Each percentage point increase in HbA1c level corresponds to an increase in average blood glucose level of about 30 mg/dL or 1.7mmol/L. As a general rule HbA1c levels above 10% represent poor diabetic control, whereas values between 6.5% and 7.5% are indicative of good control.