Interference of the most frequent haemoglobin variants on quantification of HbA1c: comparison between the LC-MS (IFCC reference method) and three routinely used methods.

AIM: Assaying HbA1c in patients with haemoglobin variants has long been a technical challenge, despite methodological advances that have progressively limited the problem. The purpose of this study was to evaluate the impact of the most frequent haemoglobin variants on three routine separation methods compared with the IFCC reference method. PATIENTS: Blood samples from heterozygous patients (AS, AC, AD, AE) were analyzed using the IFCC reference method (LC-MS), and the results compared with those obtained by capillary electrophoresis (CAPILLARYS 2 Flex Piercing, Sebia) and two HPLC methods using cation-exchange (Variant II, Bio-Rad) and affinity chromatography (Ultra(2), Primus).
RESULTS: HbA1c values obtained by the IFCC reference method were comparable to those obtained by the three tested methods whatever the haemoglobin variant. Mean relative biases did not exceed the threshold of 7% (above which differences are generally considered clinically significant), although some individual values were above this limit with Variant II in samples with HbS and for all three methods in samples with HbE.
CONCLUSION: This comparative study of the LC-MS reference method and three field methods has demonstrated that these assays are not clinically influenced by the presence of the most common haemoglobin variants. The present results also confirm that the interpretation of HbA1c values in patients with Hb variants remains complex and depends on the assays used and should, in some cases, take into account parameters other than analytical ones (such as differences in glycation rates and half-lives of haemoglobin variants).