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Rapid ELISA for PR3- and MPO-ANCA is a reliable emergency screen for small vessel vasculitis

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A rapid test for serological markers of small vessel vasculitis developed for urgent assessment is as reliable as recommended tests, according to an audit in a regional immunology laboratory in the UK. The rapid enzyme linked immunosorbent assays (ELISAs) for proteinase 3 (PR3) and myeloperoxidase (MPO) antineutrophil cytoplasmic antibodies (ANCA) are therefore suitable for emergency testing in suspected small vessel vasculitis in acute renal failure, pulmonary renal syndrome, and mononeuritis multiplex.

Good agreement was observed between the rapid (qualitative) PR3/MPO-ANCA ELISA and the international standard indirect immunofluorescence (IIF) test, with a reported sensitivity of 82%, specificity 97%, positive predictive value 92%, and negative predictive value 93%. Similar results were obtained between rapid PR3-ANCA ELISA and its standard quantitative ELISA counterpart (sensitivity 87%, specificity 93%, positive predictive value 93%, negative predictive value 88%), and complete correlation occurred between the rapid and quantitative MPO-ANCA ELISAs. Positive results in rapid and quantitative ELISAs correlated with small vessel vasculitis in all cases for which biopsy specimens were available (14 PR3-ANCA, 8 MPO-ANCA).

The audit screened serum from 103 consecutive patients over 12 months with rapid PR3- and MPO-ANCA ELISA and further tested positive samples with standard IIF and ELISA tests for ANCA. Clinical records were available for 31 of 34 patients with positive results on any test and biopsy specimens for 22.

Rapid PR3- and MPO-ANCA ELISAs are widely used in diagnostic laboratories to determine vasculitis in urgent situations but have not before been formally tested against the recommended standardised IIF and quantitative ELISA.

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