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.