title: The diagnostic value of anti-neutrophil cytoplasmic antibody testing in a routine clinical setting.
abstract: Anti-neutrophil cytoplasmic antibody (ANCA) tests are a routine clinical assay in most UK hospitals. We examined the role of routine ANCA testing in achieving a diagnosis of systemic vasculitis in a routine clinical setting. From April 1996 to March 2000, 2734 samples from five hospital departments were tested for ANCA by indirect immunofluorescence (IIF) at a single laboratory. After April 1999, enzyme-linked immunosorbent assays (ELISAs) were performed on all IIF-positive samples. Clinical diagnosis was determined for all patients with a positive IIF ANCA, and a sample of the ANCA-negative patients. Some 2-18% of patients with suspected ANCA-associated systemic vasculitis (AASV) had positive IIF ANCA. The AASV diagnosis was confirmed in 0-56% of these cases. Analysis by department suggested that 88-100% of patients with a positive IIF ANCA did not have AASV, except in the Rheumatology department. The positive predictive value (PPV) of IIF ANCA for AASV was 59% and the negative predictive value (NPV) was 84%. Of the patients with proven AASV, 41% did not have ANCA on IIF. Combined ANCA testing by IIF/ELISA had a higher sensitivity and PPV but lower specificity than IIF alone for AASV. For the combined IIF/ELISA test, only the Rheumatology department had a sensitivity or PPV >0% for AASV. The PPV of ANCA by IIF/ELISA for AASV was 79% and the NPV was 63%. The ANCA test is being widely applied with very poor return. Guidelines for more effective usage are proposed.
authors.affiliation: Rheumatic Diseases Unit, Western General Hospital, Edinburgh, UK.
authors.forename: J S
authors.initials: JS
authors.lastname: McLaren
authors.forename: R H
authors.initials: RH
authors.lastname: Stimson
authors.forename: E R
authors.initials: ER
authors.lastname: McRorie
authors.forename: J E
authors.initials: JE
authors.lastname: Coia
authors.forename: R A
authors.initials: RA
authors.lastname: Luqmani
mesh_terms: D019268:Antibodies, Antineutrophil Cytoplasmic / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D004797:Enzyme-Linked Immunosorbent Assay / Q000592:standards; D005455:Fluorescent Antibody Technique / Q000592:standards; D006801:Humans; D012680:Sensitivity and Specificity; D014657:Vasculitis / Q000097:blood / Q000175:diagnosis*
chemical_list: D019268:Antibodies, Antineutrophil Cytoplasmic; D015415:Biomarkers