Two novel haemoglobin variants that affect haemoglobin A1c measurement by ion-exchange chromatography.

BACKGROUND: Haemoglobin (Hb) variants are well-known factors interfering with accurate HbA1c testing. This report describes two novel Hb variants leading to inappropriate quantification of HbA1c by ion-exchange chromatography. METHODS: Glycated forms of novel Hb variants were recognised in the blood of two patients with diabetes mellitus screened by HbA1c ion-exchange chromatography. Dedicated high-resolution cation-exchange chromatography and subsequent DNA sequencing revealed the exact nature of the variants. Other common techniques for quantifying HbA1c were applied on both samples and haematological parameters were determined to judge possible pathology associated with the novel Hb variants. RESULTS: A fraction of 15% of abnormal Hb was observed in a 37-year-old female. DNA sequencing revealed a heterozygous mutation in the α1-globin gene, resulting in a leucine-to-phenylalanine amino-acid substitution (HBA1: c.301C>T, p.Leu101Phe). We named this variant Hb Weesp. The other novel variant, Hb Haelen, presented as a 40% fraction in a 63-year-old male and resulted from a heterozygous amino acid substitution in the ß-globin gene (HBB: c.335T>C, p.Val112Gly). The presence of both Hb variants resulted in aberrant separation of the Hb components, leading to an inadequate quantification of HbA1c. CONCLUSIONS: Close examination of HbA1c chromatograms revealed two novel, clinically silent Hb variants that interfere with HbA1c quantification. Healthcare providers need to be aware of the potential of such Hb variants when interpreting HbA1c results.

Hemoglobin analyses in the Netherlands reveal more than 80 different variants including six novel ones.

More than 20,000 blood samples of individuals living in The Netherlands and suspected of hemolytic anemia or diabetes were analyzed by high resolution cation exchange high performance liquid chromatography (HPLC). Besides common disease-related hemoglobins (Hbs), rare variants were also detected. The variant Hbs were retrospectively analyzed by capillary zone electrophoresis (CZE) and by isoelectric focusing (IEF). For unambiguous identification, the globin genes were sequenced. Most of the 80 Hb variants detected by initial screening on HPLC were also separated by capillary electrophoresis (CE), but a few variants were only detectable with one of these methods. Some variants were unstable, had thalassemic properties or increased oxygen affinity, and some interfered with Hb A2 measurement, detection of sickle cell Hb or Hb A1c quantification. Two of the six novel variants, Hb Enschede (HBA2: c.308G > A, p.Ser103Asn) and Hb Weesp (HBA1: c.301C > T, p.Leu101Phe), had no clinical consequences. In contrast, two others appeared clinically significant: Hb Ede (HBB: c.53A > T, p.Lys18Met) caused thalassemia and Hb Waterland (HBB: c.428C > T, pAla143Val) was related to mild polycytemia. Hb A2-Venlo (HBD: c.193G > A, p.Gly65Ser) and Hb A2-Rotterdam (HBD: c.38A > C, p.Asn13Thr) interfered with Hb A2 quantification. This survey shows that HPLC analysis followed by globin gene sequencing of rare variants is an effective method to reveal Hb variants.

Multicentre evaluation of the Tosoh HbA1c G8 analyser.

BACKGROUND: We report a Dutch-Belgian multicentre evaluation of the Tosoh HLC-723G8 glycohaemoglobin analyser, an ion-exchange HPLC instrument for the separation and quantification of haemoglobin A1c (HbA1c) in whole blood. METHODS: We evaluated the analytical performances of the Tosoh G8 analyser and compared the results for blood samples with its predecessor, the Tosoh G7, and with two other widely used analysers, the Bio-Rad Variant II and Adams Arkray HA-8160. RESULTS: Within- and between-batch imprecision [coefficient of variation (CVs)] was <0.5% and 2%, respectively, and compared favourably with the G7. The excellent performances in terms of speed (1.6 min/analysis) did not result in increased variability of the results or carry-over between samples. The method shows no interference from carbamylated haemoglobin, and recognises the presence of haemoglobinopathies, which triggers the correction of the HbA1c result. Comparison with established methods showed good correlation, not only with the G7 but also with the Variant II and HA-8160 systems. CONCLUSIONS: With respect to reproducibility, chromatographic resolution, speed of analysis and identification of Hb variants, the Tosoh G8 analyser can be considered to be state of the art.