Further evaluation of the world health organization international reference reagent for Haemoglobin A₂ measurement

The accurate measurement of HbA₂ is essential for the detection of β-thalassaemia carriers and as no single calibrant is used by the various manufacturers of analysers, differences are seen in results obtained. The World Health Organization International Reference Reagent for HbA₂ (WHO IRR 89/666) was made available to diagnostic laboratories in the 1980s and remains the only international reference material available. A previous study (2015) demonstrated that the WHO IRR remained suitable for use as an HbA₂ standard as tested by 52 participants in the UK NEQAS Haematology Abnormal Haemoglobins Programme. This study was undertaken to include simultaneous analysis of three whole blood specimens over a range of HbA₂ values with the WHO IRR and to include participants from laboratories outside of the UK.

Three whole blood specimens with HbA₂ levels ranging from 2.4% to 5.7% and the WHO IRR were distributed to 56 laboratories located in 14 different countries. Participants were requested to test the specimens at defined intervals and return results accompanied by chromatograms or electropherograms produced.

Differences found in results from different analyser groups reflect the bias found in the 2015 study in that bias is seen according to the methodology used and also varies in relation to the level of analyte being measured.

Results of measurements from whole blood specimens and the lyophilized WHO IRR standard did not show any deterioration of the IRR, and it remains suitable for use. Linearity and calibration of analysers remain a problem.