Committee on Diabetes Mellitus Indices of the Japan Society of Clinical Chemistry-recommended reference measurement procedure and reference materials for glycated albumin determination

Background Glycated albumin is an intermediate glycaemic control marker for which there are several measurement procedures with entirely different reference intervals. We have developed a reference measurement procedure for the purpose of standardizing glycated albumin measurements. Methods The isotope dilution liquid chromatography/tandem mass spectrometry method was developed as a reference measurement procedure for glycated albumin. The stable isotopes of lysine and fructosyl-lysine, which serve as an internal standard, were added to albumin isolated from serum, followed by hydrogenation. After hydrolysis of albumin with hot hydrochloric acid, the liberated lysine and fructosyl-lysine were measured by liquid chromatography/tandem mass spectrometry, and their concentrations were determined from each isotope ratio. The reference materials (JCCRM611) for determining of glycated albumin were prepared from pooled patient blood samples. Results The isotope dilution-tandem mass spectrometry calibration curve of fructosyl-lysine and lysine showed good linearity (r=0.999). The inter-assay and intra-assay coefficient of variation values of glycated albumin measurement were 1.2 and 1.4%, respectively. The glycated albumin values of serum in patients with diabetes assessed through the use of this method showed a good relationship with routine measurement procedures (r=0.997). The relationship of glycated albumin values of the reference material (JCCRM611) between these two methods was the same as the relationship with the patient serum samples. Conclusion The Committee on Diabetes Mellitus Indices of the Japan Society of Clinical Chemistry recommends the isotope dilution liquid chromatography/tandem mass spectrometry method as a reference measurement procedure, and JCCRM611 as a certified reference material for glycated albumin measurement. In addition, we recommend the traceability system for glycated albumin measurement.