title: A critical evaluation of commercial immunoassays for antineutrophil cytoplasmic antibodies directed against proteinase 3 and myeloperoxidase in Wegener's granulomatosis and microscopic polyangiitis.
abstract: OBJECTIVE
  To evaluate the performance of 11 commercial enzyme-linked immunosorbent assay (ELISA) kits for the detection of antineutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) and myeloperoxidase (MPO) in patients with Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA).
  
  
  METHODS
  Serum samples were taken from 92 patients with a histological and clinical diagnosis of WG (n=50) or MPA (n=42) and from 30 disease controls (systemic lupus erythematosus, n=15; rheumatoid arthritis, n=15) and 30 healthy controls. Each of the sera was tested for the presence of ANCA directed against PR3 and MPO using 11 commercially available direct ELISA kits, our in-house PR3- and MPO-ANCA capture ELISAs, and the indirect immunofluorescence technique (IFT).
  
  
  RESULTS
  In tests for WG using PR3-ANCA, the commercial direct ELISA kits differed widely in their sensitivity (from 22 to 70%) and negative predictive value (NPV) (from 43 to 70%), but only moderately in their specificity (from 93 to 100%) and positive predictive value (PPV) (from 93 to 100%). The highest sensitivity (74%) and specificity (100%) for PR3-ANCA were obtained with the in-house capture ELISA. Similar differences and trends were noted for MPO-ANCA assays. Diagnostic sensitivity was more than 60% for four and at least 50% for six of the 11 ELISA kits. The PPV varied from 84 to 100% and the NPV from 58 to 70%. In tests for MPA, the MPO-ANCA ELISA kit designated F and the in-house capture ELISA were best (both had sensitivity 62% and specificity 100%). For both WG and MPA, maximum sensitivity for ANCA was obtained with IFT (80 and 70% respectively).
  
  
  CONCLUSIONS
  Determination of PR3-ANCA and MPO-ANCA with the commercial direct ELISA kits achieved poor sensitivity for both WG and MPA. The in-house PR3 and MPO-ANCA capture ELISAs performed better than the commercial ELISAs, combining higher specificity with similar sensitivity. IFT remains the best method for ANCA detection in both diseases.
authors.affiliation: Department of Rheumatology, University of Lübeck and Rheumaklinik Bad Bramstedt, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Csernok
authors.forename: D
authors.initials: D
authors.lastname: Ahlquist
authors.forename: S
authors.initials: S
authors.lastname: Ullrich
authors.forename: W L
authors.initials: WL
authors.lastname: Gross
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019268:Antibodies, Antineutrophil Cytoplasmic / Q000032:analysis*; D016022:Case-Control Studies; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D014890:Granulomatosis with Polyangiitis / Q000097:blood* / Q000276:immunology; D006801:Humans; D008297:Male; D008875:Middle Aged; D053146:Myeloblastin; D009195:Peroxidase / Q000276:immunology*; D011237:Predictive Value of Tests; D012372:ROC Curve; D011933:Reagent Kits, Diagnostic; D012016:Reference Values; D012680:Sensitivity and Specificity; D012697:Serine Endopeptidases / Q000276:immunology*; D014657:Vasculitis / Q000097:blood* / Q000276:immunology
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D011933:Reagent Kits, Diagnostic; D009195:Peroxidase; D012697:Serine Endopeptidases; D053146:Myeloblastin