Objectives: Standardization of myositis specific antibody (MSA) detection is of high importance because these antibodies are relevant for diagnosis and stratification of patients with idiopathic inflammatory myositis (IIM) and have the potential to be used in classification criteria. Many laboratories rely on immunoprecipitation (IP) for the detection of MSA but this approach is compromised by logistic, standardization, and regulatory challenges. Therefore, reliable alternatives to IP are mandatory. Here we aimed to compare three methods for the detection of MSA. Methods: Our study initiated from a cohort of 1,619 IIM patients (BIRD/University of Bath serology service and UKMyoNet cohorts) and resulted in 157 unique serum samples enriched for higher prevalence of MSA characterized by the laboratory's routine methods, IP and line immunoassay (LIA: Euroimmun). All samples were tested using a novel fully automated particle-based multi-analyte technology (PMAT, Inova Diagnostics, research use only). Analyses included antibodies to PL-7, PL-12, SRP, NXP2, Mi-2, SAE, EJ, MDA5, TIF1γ, SRP, NXP2. Results: Overall high agreements were observed between novel methods (LIA and PMAT) and IP (Cohen's kappa 0.46–0.96) for the detection of MSA. Lowest level of agreement was found for EJ and highest for SAE. Conclusion: The data hold promise for advancements in standardization of MSA assays as well as for the potential inclusion of MSA in future classification criteria.
Objectives The objective of this study was to compare the results obtained from different assays for the detection of anti-Mi-2 antibodies, which are important markers in the diagnosis of DM. Methods The study included 82 patients (68 females/14 males), most of whom had DM (n = 57), followed by PM (n = 16) and juvenile DM (n = 9). All samples were tested using a novel particle-based multi-analyte technology (PMAT) (Inova Diagnostics, research use only) in parallel with a line immunoassay (LIA: Euroimmun). To assess clinical specificity for the PMAT assay, a total of 775 disease and healthy controls were tested. Results 29 samples were positive by at least one test for anti-Mi-2 antibodies. Of those, 24 were Mi-2β LIA+, five were Mi-2α LIA+ and 23 Mi-2 PMAT+. The comparison shows varying agreement between the different methods (kappa 0.27–0.77). When LIA results were used as reference for receiver operating characteristics analysis, high area under the curve values were found for both PMAT vs LIA Mi-2α and LIA Mi-2β. When analysing the results in the context of the myositis phenotype, PMAT associated closest with the DM phenotype. In the control group, 3/775 controls (all low levels) were anti-Mi-2+ resulting in a sensitivity and specificity of 28.1% and 99.6%, respectively. Conclusion Overall, good agreement was found between LIA and PMAT for anti-Mi-2 antibodies, which is important for the standardization of autoantibodies. Anti-Mi-2β antibodies measured by PMAT tend be more highly associated with the clinical phenotype of DM.
BackgroundMyositis specific antibodies (MSA) represent important diagnostic tools and also help stratify idiopathic inflammatory myositis (IIM) patients with particular clinical features, treatment responses, and disease outcomes. Standardization of MSA detection is of high importance because these antibodies also have the potential to be used in classification criteria.ObjectivesThe objective of this study was to evaluate the clinical performance of a novel particle based multi-analyte technology (PMAT) for the detection of MSA as an aid in the diagnosis and also in the differentiation of IIM subtypes.MethodsThe study included 464 patient samples collected at Hospital Vall d’Hebron, Autonomous University of Barcelona, most of whom had a diagnosis of IIM (n=264). As controls, samples from patients with myositis like conditions (ML, n=20), rheumatoid arthritis (RA, n=33), systemic lupus erythematosus (SLE, n=40), Sjögren’s syndrome (SjS, n=25), infectious diseases (ID, n=40) and healthy individuals (HI, n=42) were included. All samples were tested using a novel fully automated particle-based multi-analyte technology (PMAT, Inova Diagnostics, research use only; Jo-1, PL-7, PL-12, EJ, Mi-2b, NXP2, SAE, TIF1y, MDA5, HMGCR, SRP) which utilizes paramagnetic particles with unique signatures and a digital interpretation system.Abstract THU0346 –Table 1ResultsThe sensitivity/specificity of the individual MSA were: 19.7%/100% (Jo-1), 7.2%/100.0% (Mi-2), 3.0%/99.0% (NXP2), 3.8%/100.0% (SAE), 2.7%/100.0% (PL-7), 1.9%/99.5 (PL-12), 1.1%/100.0% (EJ), 15.5%/99.5% (TIF1y), 8.3%/98.5% (MDA5), 6.1%/99.0% (HMGCR) and 1.9%/98.5% (SRP). The overall clinical performance was: sensitivity 68.2% (95% confidence interval 62.3-73.5%), specificity 94.0% (95% CI 89.8-96.5%) and odds ratio 33.8. In the table below, the sensitivity and specificity of each analyte for IIM subtypes was calculated along with odds ratio.ConclusionThe novel PMAT used to detect a spectrum of MSA in IIM on a fully automated system showed good sensitivity and specificity in line with the known associations of MSA. Sensitivities and specificities of the individual MSA are within expected ranges. Lastly, the individual markers help to stratify patients into IIM subtype which is important for management of the patients.Disclosure of InterestsMichael Mahler Employee of: Inova Diagnostics (Not pharmaceutical, diagnostics company), Kishore Malyavantham Employee of: Inova Diagnostics, Michaelin Richards Employee of: Inova Diagnostics, Chelsea Bentow Employee of: INOVA Diagnostics, Silvia Casas Employee of: Inova Diagnostics, Eva Balada: None declared, Maite Sanz: None declared, M. Angeles Martinez: None declared, Albert Selva-O’Callaghan: None declared
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