2020 Volume 23 Issue 2 Pages 88-95
Many of the structural variants of hemoglobin (Hb) are caused by a single amino acid substitution resulting from point mutations within the coding sequences of globin genes. Although the majority of Hb variants do not cause disease, the presence of variant Hb can affect the values of Hb A1c measured by high-performance liquid chromatography (HPLC), as variant Hb is variably charged, thus hindering chromatographic separation. In May 2015, we introduced a fully automated Hb A1c analyzer based on HPLC, HA-8180V (Arkray), mounting not only the standard Fast Mode, but also the Variant Mode software, enabling the detection of Hb S and Hb C, and flag-marking Hb D and Hb E. As the HPLC chromatograms of four patients suggested the presence of variant Hb, we performed nucleotide sequencing of the globin genes, confirming the corresponding missense mutations. These included Hb Q-Iran (α2 75[EF4] Asp>His HBA2:c.226G>C) in two patients, Hb St. Luke’s (α1 95[G2] Pro>Arg HBA1:c.287C>G) in one patient, and Hb Toranomon (β112[G14] Cys>Trp HBB:c.339T>G) in one patient. In four Southeast Asian patients, their chromatograms matched the pattern of Hb E, which is frequent on the Indian subcontinent and in Southeast Asia. Regarding the Hb A1c values, the Variant Mode was considered to yield true values in the Hb Q-Iran and Hb St. Luke’s cases, whereas both modes presented false low values in the Hb Toranomon case. For Hb E, the HA-8180V is designed to automatically output corrected Hb A1c values. When laboratory technologists observe a chromatogram pattern suggesting the presence of variant Hb, the physicians need to be provided with information regarding the effects of variant Hb on the values of Hb A1c, and offered other monitoring markers of diabetes to make an accurate diagnosis and enable appropriate treatment.
