Antinuclear antibody (ANA) positivity pattern by line immunoassay in a hospital from eastern India: Update from a laboratory perspective

Abstract

ABSTRACT The existence of more than one antibody in systemic autoimmune rheumatic diseases (SARDs) or connective tissue disease (CTD) along with features of more than one autoimmune disease (AD) in an individual is suggestive of overlap syndrome (OS). Line immunoassay (LIA) can target many autoantibodies in a single approach, thus making the identification of OS feasible. This study aimed to identify the pattern of distribution of antinuclear antibodies by LIA prevalent in a hospital population in eastern India and identify common forms of SARD in this belt based on laboratory findings. A total of 1660 samples received for ANA profile testing by LIA were analysed. Factor analysis was performed with factor loading scores used in the k-means algorithm to identify clustering of various autoantibodies. U1-snRNP positivity was the highest at 16.69%, and the least frequent autoantibody noted was anti-Jo-1 at 0.71% positivity. Based on the outcome of factor analysis, three clusters were determined. Cluster 1 showed a predominance of anti-PM/Scl antibodies, cluster 2 showed a predominance of anti-dsDNA, anti-histone, anti-SmD1, anti-nucleosomes, anti-PCNA, anti-Po, anti-SSA/Ro52, anti-SSA-Ro60, anti-SSB/La, anti-Scl-70, anti-Mi-2, anti-Ku and anti-AMA-M2, and cluster 3 showed a predominance of anti-U1-snRNP. Mixed connective tissue disease (MCTD) and overlap syndrome (OS) are prevalent more than pure form of an AD in our study population. OS may be missed out by monospecific immunoassays and hence adds to diagnostic challenges. LIA may be more useful in identifying specific autoantibodies by a single approach rather than monospecific immunoassays in populations after a positive screen by indirect immunofluorescence (IIF).