Glycosylated (or glycated) hemoglobin (hemoglobin A1c, Hb1c , or HbA1c) is a form of hemoglobin used primarily to identify the average plasma glucose concentration over prolonged periods of time. Its name is sometimes abbreviated to A1C. It is formed in a non-enzymatic pathway by hemoglobin's normal exposure to high plasma levels of glucose. Glycosylation of hemoglobin has been implicated in nephropathy and retinopathy in diabetes mellitus. Monitoring the HbA1c in type-1 diabetic patients may improve treatment.
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Glycosylated (or glycated) hemoglobin (hemoglobin A1c, Hb1c , or HbA1c) is a form of hemoglobin used primarily to identify the average plasma glucose concentration over prolonged periods of time. Its name is sometimes abbreviated to A1C. It is formed in a non-enzymatic pathway by hemoglobin's normal exposure to high plasma levels of glucose. Glycosylation of hemoglobin has been implicated in nephropathy and retinopathy in diabetes mellitus. Monitoring the HbA1c in type-1 diabetic patients may improve treatment.
History
Hemoglobin A1c was first separated from other forms of hemoglobin by Huisman and Meyering in 1958 using a chromatographic column. It was first characterized as a glycoprotein by Bookchin and Gallop in 1968. Its increase in diabetes was first described in 1969 by Samuel Rahbar and coworkers The reactions leading to its formation were characterized by Bunn and his co-workers in 1975. The use of hemoglobin A1c for monitoring the degree of control of glucose metabolism in diabetic patients was proposed in 1976 by Koenig and coworkers.
Underlying principle
In the normal 120-day life span of the red blood cell, glucose molecules join hemoglobin, forming glycated hemoglobin. In individuals with poorly controlled diabetes, increases in the quantities of these glycated hemoglobins are noted.
Once a hemoglobin molecule is glycated, it remains that way. A buildup of glycated hemoglobin within the red cell reflects the average level of glucose to which the cell has been exposed during its life cycle. Measuring glycated hemoglobin assesses the effectiveness of therapy by monitoring long-term serum glucose regulation. The HbA1c level is proportional to average blood glucose concentration over the previous four weeks to three months. Some researchers state that the major proportion of its value is related to a rather short term period of two to four weeks.
Measuring A1c
There are a number of techniques used to measure A1c.
Laboratories use :
- high-performance liquid chromatography (HPLC)
- Immunoassay
Point of care (eg doctors surgery) devices use :
- Immunoassay
- Boronate Affinity Chromatography
POC A1c tests are certified by the National Glycohemoglobin Standardization Program (NGSP) to standardise them against the results of the 1993 Diabetes Control and Complications Trial (DCCT) .
Interpretation of results
Laboratory results may differ depending on the analytical technique, the age of the subject, and biological variation among individuals. Two individuals with the same average blood sugar can have A1C values that differ by as much as 1 percentage point. In general, the reference range (that found in healthy persons), is about 4%–5.9%.
