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

INTRODUCTION

The accurate determination of Hb A 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 A quantitation both within and between methods. The only reference material available for Hb A 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 A 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 A concentration, distributed in the same week.

RESULTS

The mean Hb A 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.