Improved Reference Measurement Method for Hemoglobin A1c by Use of Liquid Chromatography–Isotope Dilution–Tandem Mass Spectrometry

To the Editor: We have developed an improved reference measurement method for hemoglobin A1c (Hb A1c)1 based on liquid chromatography–isotope dilution–tandem mass spectrometry (LC-ID-MS/MS) with traceability to the SI unit. The method has a small measurement uncertainty (MU) and gives results in good agreement with the accuracy-based IFCC reference method. Kaiser et al. (1) demonstrated the possibility of using ID-MS for Hb A1c measurement, which involved the proteolysis of hemoglobins using endoproteinase Glu-C and hydrolysis of hexapeptide calibration standards using HCl. However, a large MU and significant difference in results compared with the IFCC reference method were observed. Using the same approach, we developed an improved procedure based on LC-ID-MS/MS and used the method for participation in an IFCC ring trial for reference laboratories (RELA 2013) for Hb A1c, in which our results for 2 lyophilized samples were compared against those from the IFCC reference method, including 6 approved IFCC network laboratories for Hb A1c. Key steps in our ID-MS procedure to preserve the unbroken traceability to …