What is hemoglobin A1c? An analysis of glycated hemoglobins by electrospray ionization mass spectrometry

Abstract

Hemoglobin A1c (HbA1c) is a stable minor Hb variant formed in vivo by posttranslational modification by glucose, originally identified by using cation exchange chromatography, and containing primarily glycated N-terminal β-chains. However, the structure(s) of the quantified species has not been elucidated, and the available methods lack a reference standard. We used electrospray ionization mass spectrometry to determine the extent of glycation of samples separated by boronate affinity and/or cation exchange chromatography. Analyses of clinical samples were consistent with the curvilinear relationship of patient glucose and HbA1c. As glycation increased, the ratio of β-chain to α-chain glycation increased, and the number of glycation sites on the β-chain increased, although these were relatively minor components. We found several glycated species that cochromatographed with HbA1c on cation exchange, including species with both glycated α- and β-chains, nonglycated α- and glycated β-chains, and multiply glycated β-chains. The combined use of affinity and cation exchange chromatography with structural confirmation by electrospray ionization mass spectrometry was found to be useful in producing samples of sufficient purity for the standardization of glycohemoglobin clinical assays.

Review of hemoglobin A1c in the management of diabetes

“…17 The components of HbA were identified by charge separation on cation exchange resin and named according to their order of elution as follows: A 0 , A 1a , A 1b , and A 1c . 18 A 1c is the Hb component that is composed chiefly, albeit to a variable degree, of glycohemoglobin. In the setting of hyperglycemia, the highly permeable erythrocyte cell membrane allows exposure of Hb to elevated intracellular glucose levels.…”

ESTIMATION OF SERUM FERRITIN LEVELS IN TYPE 2 DIABETIC PATIENTS AND ITS RELATION WITH HbA1C LEVEL.

“…Glycated hemoglobin is produced by a ketoamine reaction between glucose and the N-terminal valine of both ß-chains of the hemoglobin molecule. The major form of glycated hemoglobin is HbA 1c (4,5). According to the American Diabetes Association (ADA) guidelines, the level of HbA 1c should be kept below 7% in all the diabetics (6).…”

Glycated haemoglobin and iron deficiency anaemia: a case‐control study

“…Glycated proteins are important markers for monitoring glycaemia in patients with diabetes. 1,2 Glycated haemoglobin, whose major form is haemoglobin A1c (HbA1c), 3 is the most known and used clinical indicator for the follow up of long-term glycaemic control, and it has been recently identified as a criterion for the diagnosis of diabetes by the World Health Organization (WHO). 2 Glycated haemoglobin is formed by a spontaneous reaction between glucose and the N-terminal valine residue of both β-chains of the haemoglobin molecule.…”

“…2 Glycated haemoglobin is formed by a spontaneous reaction between glucose and the N-terminal valine residue of both β-chains of the haemoglobin molecule. 3 The glycated haemo globin produced is proportional to the plasma glucose levels, and once glycated it remains in this stable product reflecting the average level of glucose over the previous two to three months, since the red-cell lifespan is about 120 days. 4 However, HbA1c levels are influenced by various pathological conditions, such as haemolytic anaemia, 5 haemoglobino pathies, 6 and pregnancy, 7 and they are also altered by other factors, such as vitamin B12, folate and iron deficiency, [8][9][10][11][12] causing misleading interpretations of the results.…”