Diagnostic assays for Anti-PM/Scl IgG antibodies: Heterogeneity in antibody response or lack of standardization?

Background: The aim of this study was to compare the correlation between new diagnostic methodologies for detecting anti-polymyositis/scleroderma (anti-PM/Scl) IgG antibodies associated with myositis and/or systemic scleroderma assays with existing platforms. Methods: Sera from 164 samples previously tested for anti-PM/Scl IgG antibody by immunodiffusion, ID; 171 sera screened for anti-PM/Scl IgG by immunoprecipitation. IP; an additional group of 215 sera tested by ID and 46 healthy blood donor sera were retrospectively evaluated. Anti-PM/Scl IgG antibodies were measured using three PM/Scl-100 specific enzyme immunoassays (ElAs), PM1-alpha (PM1-alpha) EIA and a line immunoblot assay (LIA) for anti-PM/Scl-75 and 100 IgG antibodies. Selected samples were tested for the presence of antinuclear antibody (ANA) by indirect fluorescent antibody (IFA) assay. Results: The overall agreement between ID and all anti-PM/Scl IgG ElAs as determined by Crohnbach's alpha was unacceptable (alpha<0.50). The concordance between the IP and either LIA or PM1-alpha EIA was greater than 90% however, the best agreement was seen between the IP and LIA PM/Scl-100 assays (98.3%). Compared to the LIA PM/Scl-75 and PM1-alpha tests, the LIA PM/Scl-100 IgG assay showed the best specificity in the healthy control group. Conclusions: Our results demonstrate considerable differences between assays for detecting anti-PM/Scl IgG antibodies which cannot be attributable to heterogeneity in antibody response alone. Further characterization and standardization of these assays are needed. 2011 Elsevier B.V. All rights reserved.