Hb Westport [β121 (GH4) Glu>Asp; HBB:c.366A>C]: A novel β-globin variant interfering with HbA1c measurement

Abstract

Objectives: To describe a novel β-globin variant that interferes with HbA1c analysis by cation exchange HPLC.

Design and methods: Diabetes screening by HbA1c measurement was assessed using cation exchange HPLC and an immunoassay point-of-care analyzer. Routine hemoglobinopathy screening was performed including CBC, HbF and HbA₂ measurement by cation exchange HPLC and capillary electrophoresis (CE). Further variant characterization was undertaken by ESI TOF mass spectrometry and DNA sequencing.

Results: Discordant HbA1c results were obtained for our subject, with elevated HbA1c of 52 mmol/mol measured by cation exchange HPLC and a normal level of 34 mmol/mol by immunoassay. Abnormal HbA1c peak shape prompted hemoglobinopathy screening to investigate potential variant interference. Cation exchange HPLC (using β-thalassemia program) and CE results were apparently normal, with HbF and HbA₂ detected within reference intervals. ESI TOF mass spectrometry revealed the presence of a variant β-globin chain. A novel missense variant was confirmed at codon 121 of the β-globin gene [β121 (GH4) Glu>Asp; HBB: c.366A>C], which we have named Hb Westport.

Conclusions: Hb Westport is a novel β-globin variant that interferes with HbA1c measurement by Bio-Rad D-100 cation exchange HPLC, giving a falsely elevated result. This was clinically significant for our subject because the erroneously elevated HbA1c value was above the diabetes diagnostic threshold. Alternative methods for diabetes assessment should be considered in subjects with Hb Westport.

Keywords: Cation exchange high performance liquid chromatography (HPLC); Electrospray ionization (ESI) time-of-flight (TOF) mass spectrometry; Glycated hemoglobin (HbA1c); β-Globin variant.