Clinical applications of glycosylated haemoglobin

Glycosylated haemoglobin (HbA1c) has been in use since 1980s as the 'gold standard' for monitoring glycaemic control and as a predictor of diabetic complications. Even though several conditions, such as, haemolytic anaemia (lowers HbA1c) and aplastic anaemia (raises HbA1c) tend to confound and interfere with HbA1c measurement, in most circumstances HbA1c is a valid and reliable index of glycaemic status. Recently, HbA1c has also been recommended as a diagnostic test for diabetes mellitus by the American Diabetes Association (ADA); HbA1c offers logistical advantages over the conventional oral glucose tolerance test as it requires a non-fasting random sample. In this article the history of discovery of HbA1c, biochemical processes behind its formation, its assay techniques, various factors influencing HbA1c, importance of standardization of its assay so as to make the results reported from different laboratories much more comparable are critically reviewed. This review also provides an update on the optimal HbA1c targets, its reliability in control of diabetic complications, limitations of test results and its importance in control of diabetes patients and their complications, various cut-off values obtained in studies performed both in India and worldwide and its role as a surrogate marker of metabolic syndrome, among others.