Evaluation of the suitability of the World Health Organization International Reference Reagent for Hb A₂ quantitation (89/666) for continued use

Introduction: The accurate determination of Hb A₂ is a key marker when screening for a β-thalassaemia carrier. Data from external quality assessment (EQA) exercises have shown a lack of alignment of Hb A₂ quantitation both within and between methods. The only reference material available for Hb A₂ quantitative assay at the time of writing is the World Health Organization International Reference Reagent (89/666; WHO IRR) prepared in the 1980s and not validated for all current methodologies.

Method: The WHO IRR was analysed for Hb A₂ concentration by 52 laboratories using a representative range of high-performance liquid chromatography and capillary electrophoresis analysers. The results of the analysis were compared to those of a whole blood EQA specimen of similar Hb A₂ concentration, distributed in the same week.

Results: The mean Hb A₂ value obtained for the WHO IRR was 5.17%, compared to the assigned value of 5.3%. The range of results returned was wide (4.0%-6.2%), with differences in the results observed by between and within analyser groups. A similar range of results was seen with the whole blood sample, although the bias observed between analyser types was different from that seen with the WHO IRR.

Conclusion: The results may indicate a lack of commutability of the WHO IRR material, resulting from deterioration, matrix effects or changes in reagent formulation or calibration parameters. Further examination of the suitability of the WHO IRR (89/666) for continued use is required.