High Prevalence of Hb Riccarton Challenges HbA1c Analysis in a Danish Clinical Laboratory Using the Tosoh G11

Ion-exchange high-performance liquid chromatography (HPLC) is commonly used to measure hemoglobin A1c (HbA1c) by distinguishing it from other hemoglobin (Hb) fractions based on net charge. Hb variants can interfere with this analysis, leading to spurious HbA1c results, particularly in HPLC-based methods. This study investigated blood samples showing an HV3 peak - which indicates an Hb variant - on the Tosoh G11 chromatogram during routine HbA1c analysis in a Danish laboratory. Over 30 workdays, 53/33,006 samples displayed an HV3 peak. Sanger sequencing identified Hb Riccarton as the most common variant associated with these peaks (n = 27), consistent with its prevalence in the Danish Blood Donor Study, suggesting it is common in the Danish Caucasian population. Hb Riccarton posed a particular analytical challenge, as over half of the cases showed fluctuating HV3 peaks, initially separated from the HbA1c fraction but subsequently integrated into it upon re-analysis. In regions where Hb Riccarton is prevalent, clinical laboratories using the Tosoh G11 must be aware of this phenomenon to avoid bias and inconsistency in HbA1c reporting. Following Hb Riccarton, HV3 peaks most often indicated HbE heterozygosity (n = 16). Compared to Tosoh G11, HbA1c from the DCA Vantage showed a mean bias of -9.7% for HbE, versus -2.1% in samples without Hb variants. For Hb Riccarton, the bias was -7.2% when the HV3-peak was integrated, and +8.6% when separated from the HbA1c fraction. However, if clinicians are aware of these variants being present, both methods may be used for diabetes monitoring if applied consistently.