A rare case of variant hemoglobin (Hb yahata) suspected based on inconsistent plasma glucose and HBA1c levels

A 52-year-old man presented for an evaluation of worsening glycemic control secondary to glucocorticoid administration. The glycated hemoglobin (HbA1c) level was 8%, and oral glucose tolerance testing revealed impaired tolerance, whereas the plasma glucose and glycoalbumin levels were normal. The results of highperformance liquid chromatography (HPLC) for HbA1c, isoelectrofocusing of the hemolysate and precise HPLC measurements of the HbA1c level supported the presence of an Hb variant, and DNA sequencing of the β-globin gene revealed Hb Yahata [β112 TGT (Cys)→TAT (Tyr)] (heterozygote). In this case, the discrepancy between the plasma glucose and HbA1c levels raised suspicion of this rare Hb variant.