Effectiveness of different methods for anti-Sm antibody identification. A multicentre study

Methods for the measurement of autoantibodies frequently provide controversial results. The objective of the present study was to evaluate the performance of Spanish Clinical Laboratories in the measurement of anti-Sm antibodies. A total of 23 laboratories participated, analysing 30 serum samples from patients with systemic lupus erythematosus and other autoimmune and non-autoimmune diseases. The laboratories used four extractable nuclear antigen screens, eight enzyme-linked immunosorbent assays (ELISAs) specific for anti-Sm, one line-blot, one dot-blot and one double immunodiffusion assay, from 15 different manufacturers. A total of 871 results were obtained. In general, very good sensitivity was obtained (95-100%), but specificity was moderate (52-86%) and must be improved. Most ELISAs and the line-blot were valid assays for anti-Sm detection and could serve as tests both for analysis and/or confirmation. The likelihood ratios indicated that both methods can be considered very useful or useful for the determination of anti-Sm antibodies. Nevertheless, the analytical quality of the methods for the measurement of anti-Sm antibodies could probably be improved by standardisation of the methods and the participation of laboratories in external quality control programs.