Long-term evaluation of electrospray ionization mass spectrometric analysis of glycated hemoglobin

Background: Electrospray ionization mass spectrometry (ESIMS) has been succ essfully applied to the identification of hemoglobin (Hb) variants and the presence of glucose adducts (mass difference of 162 Dal on the separate Hb alpha and beta chains. To establish the potential of ESIMS as a routine and /or a reference method for the quantification of glycohemoglobin (HbA1c), w e carried out a detailed evaluation over a 4-month period in a routine labo ratory environment. Methods: We optimized a procedure using ESIMS suitable for the routine quan titative analysis of HbA1c. We determined reliability and reproducibility o ver 4 months and assessed the potential for automated sample injection. We then compared values of 1022 blood samples from diabetic patients with a ro utine HPLC-based ion-exchange procedure (HA-8140; Menarini). Results: Results of HbA1c measurement by ESIMS were available within 3 min. The analytical imprecision (CV) was 1.6-5.0% for both manual and automated injections. Data collection over the m/z 980-1400 range confirmed lower gl ycation of the a chain relative to the beta chain (0.66:1). Only one glycat ion was observed per globin chain. The overall glycohemoglobin (i.e., the a verage of alpha- and beta -chain glycations) measured by ESIMS (x) on 1022 blood samples was lower than by HPLC (y): y = 1.0432x + 0.4815. However, th e beta -chain glycation measured by ESIMS was up to 20% higher than the val ue measured by ion-exchange HPLC and showed a close conformity, particularl y at 5-10% HbA1c, with the ion-exchange Diabetes Control and Complications Trial (DCCT)-corrected and the United Kingdom National External Quality Ass essment Scheme DCCT mean return values. Conclusions: ESIMS provides a precise measurement of HbA1c and, in particul ar, glycation of the beta chain. The method is robust and could be proposed as a procedure to substantiate HbA1c measurement and/or calibration. (C) 2 001 American Association for Clinical Chemistry.