症例1は45歳女性。人間ドック受診時にHbA1c異常低値を指摘。HbA1cは2.9％と低値であったが，75gOGTTで耐糖能障害を認めた。GAは13.5％であった。HPLCにて異常ピークを認めた。高分離HPLCにてA0に近い位置とかなり遅い時間にも異常ピークを認め，ヘモグロビン異常症と考えられた。症例2は76歳男性，症例1の父親。糖尿病と診断されており，近医で食事療法・運動療法にて経過観察中だった。HbA1cは4.8％であったが，随時血糖は常に200mg/dL以上であった。またGAは23.4％と高値であり，血糖コントロールは不良であると考えられた。HbA1c異常低値の症例ではヘモグロビン異常症を疑うべきであり，またヘモグロビン異常症患者ではGAを血糖コントロールの指標として用いることが推奨される。

    Case1. A 45-year-old woman was referred to our hospital because of an abnormally low HbA1c level when diagnosed by routine examination. Although her HbA1c level was abnormally low (2.9%), an OGTT of 75g suggested impaired glucose tolerance. Her GA was 13.5%. When HbA1c was analyzed by the high performance liquid chromatography (HPLC) method, there was an abnormal peak on the HPLC chart. A second analysis with high quality HPLC disclosed peaks in variant hemoglobin near the A0 and at later time intervals, and the patient was strongly suspected to have variant hemoglobin. Case2. A 76-year-old man, the father of Case 1, visited our hospital for a family study. The father had diabetes mellitus and underwent diet and exercise therapies by a practitioner, but his blood glucose level was consistently above 200mg/dL. His HbA1c was 4.8%, but his GA was 23.4% and therefore his glycemic control was considered to be poor. Consequently, in cases of abnormally low HbA1c levels, we should suspect variant hemoglobin. Additionally, GA should be considered a suitable index for glycemic control for patients with variant hemoglobin.