Allergy: Evaluation of 16 years (2007–2022) results of the shared external quality assessment program in Belgium, Finland, Portugal and The Netherlands

Objectives: This paper evaluates 16 year results of the Allergy EQA program shared by EQA organisers in Belgium, Finland, Portugal, and The Netherlands. Methods: The performance of Thermo Fisher and Siemens user groups (in terms of concordance between both groups, between laboratory CV, prevalence of clinically significant errors) and suitability of samples (stability and validity of dilution of patient samples) are evaluated using data of 192 samples in the EQA programs from 2007 to 2022. Measurands covered are total IgE, screens and mixes, specific IgE extracts and allergen components. Results: There is perfect (53 %), acceptable (40 %) and poor (6 %) concordance between both method groups. In case of poor concordance the best fit with clinical data is seen for Thermo Fisher (56 %) and Siemens (26 %) respectively. The between laboratory CV evolves from 7.8 to 6.6 % (Thermo Fisher) and 7.3 to 7.7 % (Siemens). The prevalence of blunders by individual laboratories is stable for Siemens (0.4 %) and drops from 0.4 to 0.2 % for Thermo Fisher users. For IgE, the between year CV of the mean of both user groups is 1 %, and a fifteen-fold dilution of a patient sample has an impact of 2 and 4 % on the recovery of Thermo Fisher and Siemens user groups. Conclusions: The analytical performance of Thermo Fisher is slightly better than that of Siemens users but the clinical impact of this difference is limited. Stability of the sample and the low impact of dilution on the recovery of measurands demonstrates the suitability for purpose of the EQA program.info:eu-repo/semantics/publishedVersio

Analytical validation of the Hevylite assays for M-protein quantification

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Clinically relevant discrepancies between different rheumatoid factor assays

Accurate measurements of rheumatoid factors (RFs), autoantibodies binding IgG, are important for diagnosing rheumatoid arthritis (RA) and for predicting disease course. Worldwide, various RF assays are being used that differ in technique and target antigens. We studied whether assay choice leads to clinically important discrepancies in RF status and level. RF measurements using four commercial RF assays were compared in 32 RF+ samples. Using enzyme-linked immunosorbent assays (ELISAs), the influence of the target antigen source - human IgG (hIgG) versus rabbit IgG (rIgG) - on measured RF levels was investigated in arthralgia patients and RA patients. Substantial discrepancies were found between RF levels measured in the four commercial assays. Six samples (19%) with RF levels below or slightly above the cutoff in the rIgG-based Phadia assay were RF+ in three assays using hIgG as the target antigen, some with very high levels. Direct ELISA comparisons of RF reactivity against hIgG and rIgG estimated that among 173 ACPA+ arthralgia patients, originally RF negative in rIgG-based assays, up to 10% were single positive against hIgG. Monoclonal RFs binding to hIgG and rIgG or hIgG only supported these findings. In a cohort of 69 early RA patients, virtually all RF responses reacted with both targets, although levels were still variable. The use of RF assays that differ in technique and target antigen, together with the different specificities of RF responses, leads to discrepancies in RF status and levels. This has important consequences for patient care if RA diagnosis and disease progression assessments are based on RF test result