Ensuring HbA1c Accuracy and Variant Detection in Hemoglobin G-Coushatta and Queens Using Variant Mode Analysis

Background/Objectives: Glycated hemoglobin (HbA1c) is widely used to monitor glycemic control, but the accuracy and flag detection rates of HbA1c assays can vary in the presence of Hb variants such as Hb G-Coushatta (Coushatta) and Hb Queens (Queens), which are common in the Korean population. Methods: We evaluated four HbA1c platforms—Arkray ADAMS HA-8190V (HA-8190V) fast/variant modes; Tosoh HLC-723 G11 (G11) standard/variant modes; Bio-Rad D-100 (D-100); Sebia Capillarys 2 Flex Piercing (Capillarys)—using 33 Hb variant samples (26 Coushatta, 7 Queens). The Roche Tina-quant HbA1c Gen. 3 immunoassay was used as the comparative method. With UPLC-MS/MS used as the reference for variant identification, analytical performance was assessed by calculating mean % differences in HbA1c and evaluating Hb variant flag detection rates. Results: The mean % differences in HbA1c compared to the comparative method were −1.5% and −0.9% for Coushatta and Queens, respectively, with HA-8190V variant mode; −28.4% and −17.6% with HA-8190V fast mode; +33.5% and +2.2% with the G11 variant mode; −28.1% and −14.3% with G11 standard mode; −5.9% and −3.2% with D-100; and +1.0% and −6.2% with Capillarys. For flag detection, rates were 100% and 0% with HA-8190V fast mode; 84.6% and 28.6% with G11 standard mode; and 100% and 100% with all other platforms. Conclusions: Coushatta caused severe underestimation in rapid modes, while Queens hindered automated detection. While variant modes significantly improved detection, they showed platform-dependent accuracy. When Hb variant status is unknown, use of the variant mode is recommended to ensure reliable results.