HbA1c

Clinical Significance:

HbA1c is glycosylated hemoglobin also called as glycated haemoglobin, are post transitional modification of hemoglobin formed by non-enzymatic addition of a sugar residue to haemoglobin beta chain. Four species of glycated Hb are measured based on their electrophoretic mobility in clinical practice – HbA1a1, HbA1a2, HbA1b, HbA1c, collectively called as HbA1.

Formation of glycosylated hemoglobin is essentially irreversible and the blood levels depend on both the life span of red blood cell (average 120 days) and blood glucose concentration. Once glucose attaches to haemoglobin, it doesn’t let it go. It’s there for the lifetime of the red blood cell, which, in total is several months as new red blood cells are continually being made and others are dying. All this means that a glycohemoglobin test shows your average blood glucose level over the previous 6-8 weeks. It is therefore called a test with memory. Therefore, they represent integrated values for glucose over the preceding six to eight weeks. HbA1c is the major fraction constituting approximately 80% of HbA1.

Increased synthesis of haemoglobin A1c correlates with lack of glucose control; in diabetics with good glucose control, the amount of Haemoglobin A1c returns to the reference levels.  The measurement of glycated haemoglobin in the form of HbA1c has become a popular and important tool in assessing the glycemic control of diabetic patients. Its popularity is partly due to the fact that it gives clinicians an objective assessment of glucose control over the past 6-8 weeks. In addition, the test has been clinically validated by such studies as the Diabetes Control and Complications Trial (DCCT), which have shown that improved glycemic control, as measured by HbA1c, can reduce the risk of developing micro vascular and other complications of diabetes.

HbA1c can be measured in the routine laboratories from whole blood (EDTA) samples by different techniques like affinity chromatography (optimal technique), ion-exchange chromatography, electrophoresis, immunoassay and colorimetric methods. However, HPLC is regarded as the golden standard and is the trusted technique, used worldwide and also by the clinical trials done under DCCT. When measured with HPLC, HbA1c in whole blood is stable for 7 days at 4⁰C and for 3 days at 25⁰C.

The HbA1c test should be done every three to six months, depending on the treatment program and level of control of diabetes.  The ADA recommends that the HbA1c level first are measured at the time of diagnosis and initiation of treatment. Thereafter, the test should be done at least twice a year in people with non-insulin-dependent (type II) diabetes who do not use insulin; four times a year in people with insulin-dependent (type I) diabetes or those with type II diabetes who use insulin. It should be done more frequently in people with either type Type I or Type II diabe