Performance of the BMD FIDIS connective 10 ENA luminex method in external quality assurance proficiency programmes in a diagnostic laboratory setting

Objective: Despite the availability of luminex technology in the format of a commercial in-vitro diagnostic assay for anti- ENA detection, it is in routine use in only a small proportion of clinical laboratories. The purpose of this study was to establish the diagnostic performance of the BMD Connective 10 (C10) assay by reviewing the results from two independent (RCPA and UKNEQAS) EQA programmes over a three year period when placed into a routine diagnostic testing environment. Methods: Anti-ENA results (n=78 analytes) from two EQA programmes submitted over the years 2007 - 2009 as partial fulfi lment of the laboratory quality assurance systems were reviewed for compliance against target results. In addition, a representative (20% of the review period) group of routine assay quality control was reviewed. Results: For routine quality control the range of precision using multi-constituent controls across all ENA antigens was 10-17% CV. These results compared favourably with the kit supplied positive control (15% CV). Combining both EQA programs, the assay delivered 92% compliance (76/78) against target results. The two non-compliant results were two specimens from the RCPA programme reactive for PM-Scl. Non-detection of PM-Scl was an expected outcome as this antigen was not present in the panel. Conclusion: This retrospective review proves that under the conditions encountered in a routine diagnostic testing environment the C10 assay can consistently and reliably detect antibodies directed against SSA, SSB, Ro 52, Sm, Sm/RNP, Scl-70, Jo-1 and Ribo-P. In addition to excellent sensitivity against the defi ned antigens, the assay, on an evidence based approach, despite the limitation of small sample size, demonstrated good specifi city.