title: What is the clinical significance of anti-Sm antibodies in systemic lupus erythematosus? A comparison with anti-dsDNA antibodies and C3.
abstract: OBJECTIVE
  To investigate the clinical value of anti-Sm antibodies in diagnosis and monitoring of systemic lupus erythematosus (SLE) and their ability to predict lupus flares compared with that of anti-dsDNA antibody and complement (C3) assays.
  
  
  METHODS
  Autoantibodies against Smith antigen (Sm) and double-stranded DNA (dsDNA) in sera from SLE (n=232), myositis (n=26), systemic sclerosis (n=81), Sjögren's syndrome (n=88), and rheumatoid arthritis patients (n=165) and healthy donors (n=400) were determined by using enzyme-linked immunosorbent assays (both from Euroimmun). New thresholds for both autoantibodies were calculated by receiver operating characteristics (ROC) curve analysis. Cross-sectional, longitudinal and predictive analyses of anti-Sm and disease activity were also performed.
  
  
  RESULTS
  Sensitivities of 25.9% for anti-Sm (cut-off: 3.6 relative units/ml) and 30.2% for anti-dsDNA (cut-off 157.4 international units/ml) were obtained at a specificity of 99%. 14.8% of anti-dsDNA-negative patients were positive for anti-Sm, and more than half (51.4%) of anti-dsDNA-positive patients were also positive for anti-Sm. Anti-Sm antibodies were associated with age (p=0.0174), the number of ACR criteria (p=0.0242), the ACR criteria renal (p=0.0350) and neurologic disorder (p=0.0239), the BILAG category constitutional symptoms (p=0.0227), fatigue (p=0.0311) and cross-sectional disease activity (r=0.2519, p=0.0224). Although no correlations with lupus activity were observed in the longitudinal and predictive analysis, a remarkable association was found between anti-Sm and proteinuria.
  
  
  CONCLUSIONS
  Anti-Sm antibodies are essential for diagnosis of SLE, especially in anti-dsDNA-negative patients. However, our data suggest that anti-Sm monitoring is only helpful in SLE patients with active lupus nephritis.
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Flechsig
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rose
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany.
authors.forename: Fidan
authors.initials: F
authors.lastname: Barkhudarova
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany.
authors.forename: Romy
authors.initials: R
authors.lastname: Strauss
authors.affiliation: German Rheumatism Research Center Berlin-Leibniz Institute, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Klotsche
authors.affiliation: EUROIMMUN Medizinische Labordiagnostika AG, Lübeck, Germany.
authors.forename: Cornelia
authors.initials: C
authors.lastname: Dähnrich
authors.affiliation: EUROIMMUN Medizinische Labordiagnostika AG, Lübeck, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schlumberger
authors.affiliation: Department of Nephrology and Intensive Care Medicine, Charité University Hospital Berlin, Germany.
authors.forename: Philipp
authors.initials: P
authors.lastname: Enghard
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany.
authors.forename: Gerd-Rüdiger
authors.initials: GR
authors.lastname: Burmester
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany.
authors.forename: Falk
authors.initials: F
authors.lastname: Hiepe
authors.affiliation: Department of Rheumatology and Clinical Immunology, Charité University Hospital Berlin, Germany. robert.biesen@charite.de.
authors.forename: Robert
authors.initials: R
authors.lastname: Biesen
mesh_terms: D000974:Antibodies, Antinuclear / Q000276:immunology*; D016022:Case-Control Studies; D003176:Complement C3 / Q000276:immunology*; D003430:Cross-Sectional Studies; D004247:DNA / Q000276:immunology*; D006801:Humans; D008137:Longitudinal Studies; D008180:Lupus Erythematosus, Systemic / Q000175:diagnosis / Q000276:immunology*; D016017:Odds Ratio; D012372:ROC Curve; D012216:Rheumatic Diseases / Q000175:diagnosis / Q000276:immunology; D012680:Sensitivity and Specificity; D055517:snRNP Core Proteins / Q000276:immunology*
chemical_list: D000974:Antibodies, Antinuclear; D003176:Complement C3; D055517:snRNP Core Proteins; D004247:DNA