Audit of the clinical usefulness of a rapid qualitative ELISA screen for antimyeloperoxidase and antiproteinase 3 antibodies in the assessment of patients with suspected vasculitis

BACKGROUND: The need for urgent antineutrophil cytoplasmic antibody (ANCA) results when assessing patients with acute renal failure, pulmonary renal syndrome, or mononeuritis multiplex has led to the development of a rapid qualitative ELISA screening assay for antibodies to myeloperoxidase (MPO) and proteinase 3 (PR3). AIMS: To report the use of a rapid qualitative ELISA screen for PR3-ANCA and MPO-ANCA in a regional immunology laboratory and its correlation with standard indirect immunofluorescence (IIF) and quantitative ELISA for PR3-ANCA and MPO-ANCA. METHODS: Over 12 months, 103 samples requiring urgent ANCA testing were screened by a rapid qualitative ELISA and the results compared with IIF and quantitative ELISA assays for PR3-ANCA and MPO-ANCA. RESULTS: There was an excellent correlation between the rapid qualitative ELISA and standard ANCA IIF and a routine ELISA for MPO/PR3-ANCA, with sensitivities ranging from 82% to 100%. There were two false negatives, which gave weak to moderately positive values as determined by routine ELISA. However, the clinical relevance of these two cases is doubtful. CONCLUSIONS: The rapid ELISA for anti-MPO and anti-PR3 correlates well with quantitative ELISA and IIF ANCA, and urgent management decisions in patients with suspected small vessel vasculitis can be based with confidence on this test.