Authors : Das R, Muralidharan M, Mitra G, Bhat V, Mathew B, Pal D, Ross C, Mandal AK
Publication Year : 2015
Glycated hemoglobin (HbA1c), is a gold standard biomarker for assessing the glycemic index of an individual. HbA1c is formed due to nonenzymatic glycosylation at N-terminal valine residue of beta globin chain. Cation exchange (CE) HPLC is mostly used to quantify HbA1c in blood sample. A few genetic variants of hemoglobin and post-translationally modified variants of hemoglobin interfere with CE-HPLC based quantification, resulting in its false positive estimation. Using mass spectrometry, we have analyzed a blood sample with abnormally high HbA1c (52.1%) in CE-HPLC method. The observed HbA1c did not corroborate with the blood glucose level of the patient. Mass spectrometry based bottom up proteomics approach, intact globin chain mass analysis and chemical modification of the proteolytic peptides identified the presence of Hb Beckman, a genetic variant of hemoglobin, in the experimental sample. Similar surface area to charge ratio between HbA1c and Hb Beckman might have resulted in the co-elution of the variant with HbA1c in CE-HPLC. Therefore, in the screening of diabetes mellitus through the estimation of HbA1c, it is important to look for genetic variants of hemoglobin in samples that shows abnormally high glycemic index and HbA1c must be estimated using alternative method.