Trueness Evaluation and Verification of Interassay Agreement of 11 Serum IgA Measuring Systems : Implications for Medical Decisions

BACKGROUND: To identify an IgA deficiency, the availability of reliable IgA lower reference limits is essential, especially in pediatrics. In this study, we reported the results of an intercomparison study aimed to verify the status of standardization of IgA measurements using 11 commercially available measuring systems (MSs). METHODS: After confirming its commutability, the ERMDA470k/IFCC reference material was used for the trueness evaluation of IgA MSs. Furthermore, the interassay agreement was verified using 18 patient pools. By combining the bias, if any, between the obtained mean of ERM-DA470k/IFCC and its target value and the mean imprecision of MSs with the uncertainty of respective calibrators, we also estimated the mean uncertainty (U) of IgA measurements on clinical samples. RESULTS: Although the majority of IgA MSs were sufficiently aligned with each other, the bias against the ERM-DA470k/IFCC target value was unacceptable in 55% of cases. This bias resulted in an excessive U of IgA measurement on clinical samples. Importantly, when the analysis focused on the lower IgA concentrations—typical of children—the situation worsened, with only 4 MSs showing good equivalence. CONCLUSIONS: Although the harmonization among most commercially available IgA MSs is good, the implementation of traceability to higher order references is inadequate, especially at concentrations 0.7 g/L. This analytical background information needs to be considered carefully when defining traceable reference intervals in the pediatric population.