LAUSR

OBJECTIVES To evaluate the performance characteristics of a line immunoassay (LIA) for the detection of Mi-2 antibodies associated with dermatomyositis (DM). METHODS In total, 432 consecutive patient specimens were tested for Mi-2 antibodies concurrently by LIA (Mi-2α or Mi-2β) or immunoprecipitation (IP) test and antinuclear antibody by indirect immunofluorescence assay using HEp-2 substrate. Following antibody evaluation, results for patients positive in any of the assays for Mi-2 antibody had a retrospective chart review for diagnostic categorization. The performance of all tests was evaluated based on the extracted clinical data. RESULTS Forty patients were positive in at least one of the Mi-2 assays. The frequency of Mi-2β antibody by LIA was highest (75.0%), followed by Mi-2 by IP (35.0%) and Mi-2α by LIA (20.0%), respectively. Mi-2 by IP had the best total percent agreement for DM (95.0%) compared with 70.0% and 25.0% for the LIA Mi-2α and Mi-2β, respectively. Positivity of the Mi-2β antibody was significantly associated with non-DM diagnosis. CONCLUSIONS Agreement for DM with assays for detecting Mi-2 is variable. Additional studies are required to validate Mi-2 immunoassays for routine patient evaluation.