Three assays for glycohemoglobin compared

Abstract

Using 123 specimens, we compared the concordance of three different methods for determining glycohemoglobin (GHb): the Diamat(TM) (Bio-Rad Laboratories), an automated analyzer measuring HbA(1c) by cation-exchange chromatography; an assay with the IMx analyzer (Abbott Laboratories), based on boronate affinity binding; and an HPLC method measuring HbA(1c) by cation- exchange chromatography on a PolyCAT A column (PolyLC Inc.). The Pearson's correlation coefficient between PolyCAT A and Diamat was 0.900 ± 0.038 (mean ± 2 SD) and between PolyCAT A and IMx, 0.857 ± 0.042. However, up to twofold differences were seen in some samples. The proportion of GHb was consistently lower with the PolyCAT A method than with the other two assays, apparently because of better separation of HbA(1c) from nonglycated coeluting forms of Hb. The difference in glycation percentage between the PolyCAT A and Diamat methods is 2-3% over the whole concentration range. These results point to the limitations of Diamat as a reference method to be used to calibrate other methods for determining HbA(1c). Further, a switch from one method to another is likely to cause considerable problems in the clinical follow-up of certain patients.