Normal glucose tolerance with high HbA1c levels observed in two cases of Hb variants

Hemoglobin (Hb)A1c is a marker of long-term glycemic control in patients with diabetes. At the 69th Scientific Sessions of the American Diabetes Association, it was announced that the diagnosis of diabetes may be conveniently based on HbA1c ≥6.5%, without the need to measure plasma glucose concentration (International Expert Committee in Diabetes Care 32:1327–1334, 2009). However, we experienced two cases of high HbA1c levels with normal glucose tolerance confirmed by 75 g oral glucose tolerance test (75 g OGTT); thus, these cases might have been misdiagnosed as diabetes if we had not measured plasma glucose levels. If HbA1c is used as the sole means of diagnosis and assessing the glycemic state, some patients with hemoglobinopathy will be misdiagnosed as having diabetes, which could lead to unnecessary treatment. Importantly, medical staff should be aware of the limitations of measurement of HbA1c by the HPLC method with respect to interference with Hb variants. Concomitant use of other glycemic markers such as plasma glucose or glycoalbumin is recommended when the value of HbA1c is considered unreliable.