WHAT TO REPORT? GLYCATED HAEMOGLOBIN
(HBA1c) STANDARDIZATION
By Dr Annalise E Zemlin and Prof Rajiv T Erasmus,Division of Chemical Pathology,National Health Laboratory Services and University of Stellenbosch,Tygerberg Hospital, Cape Town, South Africa
WHAT IS HBA1c? In 1949, Linus Pauling described the existence of haemoglobin variants for the first
time.After years of research, the process of glycation was understood and glycosylated haemoglobin described in 1966. In 1969, Samuel Rahbar and co- workers showed that these haemoglobin fractions were increased in diabetics. Since then numerous research has been performed on HbA1c and it has been used as the gold-standard for glycaemic control follow-up in diabetics for over three decades. It is important to differentiate between glycosylation, which is the enzymatic attachment of sugars to a protein and alters the surface
34
www.lifesciencesmagazines.com
activity, receptor binding capabilities and degradation properties amongst others of the protein, and glycation, which refers to the nonenzymatic attachment of glucose to protein leading to the formation of glycated proteins, which are heterogeneous and nonspecific. HbA1c is formed when haemoglobin
A, the major component of adult haemoglobin, is modified by the covalent attachment of glucose to the amino terminus of the β-globin
chain.This reaction occurs via glycation, i.e. it is spontaneous. HbA1c is used for glycaemic control follow-up for the last 120 days (the average life-span of the erythrocyte), as its concentration is dependent on the glucose
concentration in the blood.Obviously, the determination of HbA1c for this purpose will be unreliable if the erythrocyte life span is affected such as in erythrocyte disorders, haemolytic anaemias or iron deficiency or if there are haemoglobin abnormalities such as the thalassaemias.Other factors that affect the HbA1c concentrations may be renal failure, high and low glycators and racial and ethnic differences.
RECOMMENDATIONS FOR HBA1c TESTING HbA1c has been used to give an indication of glycaemic control for over three decades. TheAmerican DiabetesAssociation (ADA) recommends an HbA1c level of 4-6% in
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40