A Case With Falsely Elevated HbA1c Concentration Caused by Unknown Modified Hemoglobin

Abstract

We herein describe a case with a falsely high HbA1c level due to modified hemoglobin. A 72-year-old man visited our clinic to evaluate his diabetes status. Although an OGTT revealed impaired glucose tolerance and a glycated albumin level of 16.4 %, the HbA1c value measured by high-performance liquid chromatography (HPLC) was high (8.1 %) and an abnormal peak on its chromatogram was observed. On the other hand, the HbA1c values measured by an immunoassay and enzyme assay were 2.4 % and 4.0 %, respectively. An analysis by high-resolution HPLC (KO500) showed two abnormal peaks at near labile HbA1c and between HbA and HbA1c. However, an analysis of the globin gene including α-chain and β-chain showed no mutation. The two abnormal peaks observed in KO500 were analyzed using mass spectrometry. Consequently, both were revealed to be β-globin with a modified molecule of 88 Da. Although the nature of this molecule is unknown, it differs from known modified hemoglobin due to its molecular weight. This may be a new condition with a falsely high HbA1c level.