Effects of 49 Different Rare Hb Variants on HbA1c Measurement in Eight Methods

Background: Previous studies have shown interference with HbA1c measurement from the 4 most common heterozygous Hb variants (HbAS, HbAE, HbAC, and HbAD) with some assay methods. Here we examine analytical interference from 49 different less common variants with 7 different HbA1c methods using various method principles. Methods: Hb variants were screened using the Bio-Rad Variant or Variant II beta thal short program, confirmed by alkaline and acid electrophoresis, and identified by sequence analysis. The Trinity ultra2 boronate affinity high-performance liquid chromatography (HPLC) method and Roche Tinaquant immunoassay were used as primary and secondary comparative methods, respectively, since these methods are least likely to show interference from Hb variants. Other methods included were the Tosoh G7 and G8, Bio-Rad D-10 and Variant II Turbo, Diazyme Enzymatic, and Sebia Capillarys 2 Flex Piercing. To eliminate any inherent calibration bias, results for each method were adjusted using regression verses the ultra2 with nonvariant samples. Each method’s calibration-adjusted results were compared and judged to be acceptable if within the 99% prediction interval of the regression line for nonvariant samples. Results: Almost all variant samples were recognized as such by the ion-exchange HPLC methods by the presence of abnormal peaks or results outside the reportable range. For most variants, interference was seen with 1 or more of the ion-exchange methods. Following manufacturer instructions for interpretation of chromatograms usually, but not always, prevented reporting of inaccurate results. Results: Laboratories must be cautious about reporting results when the presence of a variant is suspected.