A 52-year-old woman with a medical history of hepatitis B, hyperlipidemia, hypertension, anemia, and depression presented to the internal medicine clinic for a routine visit. Laboratory tests 3 months previously had revealed an impaired fasting glucose concentration of 5.9 mmol/L (106 mg/dL) [reference interval, 3.9–5.6 mmol/L (70–100 mg/dL)]. Therefore, a hemoglobin (Hb)2 A1c analysis was performed. The initial Hb A1c evaluation by cation-exchange HPLC (CE-HPLC) (Hb A1c Program on the VARIANT II TURBO Link System; Bio-Rad Laboratories) showed an Hb A1c value of 115.8% (reference interval, 4.0%–6.0%) (Fig. 1).