Standardization Challenges in Glycated Albumin Measurement: Methodological Heterogeneity and Quantification Discrepancies

BACKGROUND: Glycated albumin (GA) is a valuable biomarker for monitoring glycemic status. However, measurement standardization is challenged by methodological heterogeneity, where different analytical principles and target measurands cause quantification discrepancies. This study systematically compared prevailing methodologies to identify a robust reference measurement procedure for widespread standardization. METHODS: We compared a targeted bottom-up proteomics method (ID-LC-MS/MS) with an enzymatic assay and the Japan Society of Clinical Chemistry (JSCC) reference method. A cohort of 129 donor serum specimens and certified reference materials (JCCRM-611) were analyzed to assess methodological comparability. Furthermore, GA concentration-dependent glycation kinetics at the Lys-525 site of albumin was examined. RESULTS: The optimized targeted bottom-up proteomics method showed a strong correlation (r = 0.986) with both the enzymatic assay and JSCC reference method. However, a progressively increasing negative systematic bias was observed at higher GA levels, confirming that Lys-525 underestimates GA at higher levels. In addition, with increasing overall GA concentration, the glycation ratio at the Lys-525 site consistently declined compared to the total glycated lysine residues. CONCLUSIONS: The standardization of GA measurements requires a precise, universally accepted definition to address analytical discrepancies. The present results indicate that quantification targeting all glycated lysine residues (as in the JSCC method) aligns more closely with biologically relevant GA values than site-specific measurement at Lys-525, which shows greater bias at higher concentrations. Therefore, further GA standardization would focus on adopting total glycated lysine residues on albumin as the preferred measurand definition, to improve detection accuracy and clinical comparability.