3 cases of variant hemoglobin Hb A2-Niigata detected by falsely high HbA1c values.

Background: HbA1c measurements in blood are used to monitor diabetes status.

Methods: We detected 3 cases (1 diabetic case, 1 borderline diabetic case, and 1 case with normal glucose tolerance) of variant hemoglobin Hb A2-Niigata based on falsely high HbA1c values measured by high-performance liquid chromatography (HPLC).

Results: In all 3 cases, HbA1c values measured by the HPLC method were higher than the reference range whereas the HbA1c values measured by immunoassay, plasma glucose and glycated albumin were within the reference range. The results of the genetic test revealed heterozygous mutation GTG (Val) → GCG (Ala) in codon 1 of the δ-globin gene in all 3 cases, based on which Hb A2-Niigata was found. Although until now Hb A2-Niigata has been reported in 3 cases, this is the first report on Hb A2-Niigata with falsely high HbA1c values.

Conclusions: In this report, 3 cases of Hb A2-Niigata were found in a single institution in a short period; therefore, Hb A2-Niigata would exist frequently in a certain area. As a pathology causing falsely high HbA1c values, Hb A2-Niigata should be kept in mind.