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.

Survey and assessment of the actual state of routine measurement of glycohaemoglobin/GHb by commercial methods: warning to the users and the providers

As the clinical availability of glycohaemoglobin/GHb measurement increases, so does the need for comparable and accurate values among different laboratories and different methods. At least there should be comparability, i.e., commutability or feasibility of providing comparable results from different assays in different laboratories. A clinical joint study on insulin therapy, a survey of the actual inter-laboratory differences in GHb measurement among 41 institutions and an assessment of 11 assay methods for the determination of GHb were performed using commercial calibrators and fresh blood samples. Data on the actual state of inter-laboratory and inter-assay differences of observed values were useful for comparing results among facilities. The recommendation of the Japan Diabetes Society to measure only the stable GHb component and to correct the GHb percentage by two-point calibration with assigned values, was effective but not sufficient. Even after correction, 8 out of 11 methods still remained of little practical use because of their large relative errors. Inter-method differences among 11 available assay methods were great even after correction and depended on not only the methods but the samples used for the determination. The performance of some methods or instruments used are only poor at distinguishing the stable glycated haemoglobin itself. Some alternative measurement system with comparability, commutability and precision should be established. An urgent and worldwide problem to remove inter-laboratory differences in the measurement of GHb needs to be solved. Users in clinical practice must recognize these problems, and, before supply, the providers should check their method and keep records that are readily traceable.