Nicola Bizzaro, Italy
Azienda Sanitaria Universitaria Integrata di Udine Laboratory of Clinical PathologyPresenter of 2 Presentations
SCREENING AND DISEASE-ORIENTED PROFILES IN THE DIAGNOSIS OF AUTOIMMUNE RHEUMATIC DISEASES.
ASSIGNING LIKELIHOOD RATIOS TO IMMUNOBLOT ASSAY RESULTS: A CLINICAL APPROACH IN AUTOIMMUNE REPORTING
Abstract
Background and Aims
Recent studies showed how using likelihood ratios (LRs) to report autoantibodies results may improve their clinical interpretation. We aimed to assess whether LR calculation could be extended to antibodies to anti-extractable nuclear antigens (ENA) tests results, carried out by immunoblot (IB).
Methods
We evaluated result specific LRs for the ENA profile (Sm, RNP, Ro60, Ro52, Scl70, Jo1 and CENP-B) by an immunodot method (BlueDiver Quantrix, D-tek, Belgium) on 269 diagnostic samples from patients with ANA-associated autoimmune rheumatic diseases (AARD) [systemic lupus erythematosus (SLE) (n=79), primary Sjögren’s syndrome (SjS) (n=97), systemic sclerosis (SSc) (n=69), idiopathic inflammatory myositis (IIM) (n=12), mixed connective tissue disease (MCTD) (n=12)], and samples from 117 controls (81 diseased controls and 30 healthy blood donors).
Results
We calculated the LRs for each single anti-ENA antibody and for all antibodies grouped together, defining LR at different thresholds (Table). At 6 arbitrary units (AU) (corresponding to the cutoff indicated by the manufacturer), 12 AU, 25 AU, and 50 AU (corresponding to assay calibrators), overall positive LRs (all antibodies grouped together) for AARD were 14.5, 16.0, 41.2 and 65.0, respectively, while overall negative LRs for AARD were 0.45, 0.47, 0.54 and 0.62, respectively.
Conclusions
Our study shows that expressing results in LR is also feasible using IB methods, even if some differences may be found due to local variation in the referred population. The use of LRs in addition to antibody values may facilitate the clinical interpretation of anti-ENA IB results and may contribute to harmonizing autoimmune laboratory reporting.