The method for measurement of glycated albumin based on peptide analysis calibrated with synthetic peptides

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Based on confirmation of lysine 525 (Lys525) in albumin as the primary glycation site in a study of glycation sites on glycated albumin (GA), we determined levels of peptides containing glycated and non-glycated Lys525 in albumin, and developed a GA measurement method in which the ratio of these peptides was used as an indicator of blood glucose kinetics. Substances for measurement were defined as peptides containing glycated Lys525 (G-525Lys, Lys525- Nε-(1-deoxy-D-fructos-1-y1)-undecapeptide) and those containing non-glycated Lys525 (NG-525Lys, Lys525-undecapeptide) obtained from enzymatic hydrolysis of plasma or serum using endoproteinase Glu-C. Quantification was performed by liquid chromatography/mass spectrometry (LC/MS) using the respective synthetic peptides as calibrators. GA level was expressed as [G-525Lys/(G-525Lys + NG-525Lys)] in milimoles/mole.Within-run and day-to-day CVs were< 1.0%. Correlation coefficients between the present method and common measurement methods were > 0.97. The present GA measurement method enables GA level to be expressed in SI units.