SCREENING FOR ANTINEUTROPHIL CYTOPLASMIC ANTIBODIES (ANCA) - IS INDIRECT IMMUNOFLUORESCENCE THE METHOD OF CHOICE

Detection of ANCA has become an important tool for the diagnosis and m onitoring of disease activity in Wegener's granulomatosis (WG). Unfort unately, a group of sera positive by the standard method for ANCA dete ction, indirect immunofluorescence (IIF), are negative when more speci fic tests with purified proteins are used. In order to examine this di screpancy we examined groups of sera selected for being (i) C-ANCA-pos itive by IIF; (ii) positive in proteinase 3 (PR3)-ANCA ELISA; and (iii ) from 24 patients with WG. The following assays were used: IIF, PR3-A NCA ELISA and capture PR3-ANCA ELISA using MoAbs against PR3. Furtherm ore, since granule enzymes are released during coagulation, we also me asured ANCA in complex with PR3. To test if granule enzyme release had any influence on ANCA detection, both serum and EDTA-plasma were coll ected from a patient with active WG. No difference, however, was found . In the IIF-positive group (n = 60) 68% of the sera were positive in PR3-ANCA ELISA, 86% in capture PR3-ANCA ELISA and 80% were positive fo r the PR3/IgG-ANCA complex. In the PR3-ANCA ELISA group (n = 105) 88% of the sera were positive by IIF, 98% in capture PR3-ANCA ELISA and 53 % in the PR3/IgG-ANCA assay. To evaluate the tests clinically sera fro m 24 patients with WG were examined. In the remission group (n = 10) t wo patients were positive by IIF, four in the PR3-ANCA ELISA, and five in the capture PR3-ANCA ELISA. Fourteen had active disease, and in th is group 11/14 were positive by IIF, 10/14 in PR3-ANCA ELISA and 12/14 by capture-ELISA. The correlation between IIF and capture PR3-ANCA EL ISA titre (r = 0.72, P = 0.0095) was better than between PR3-ANCA ELIS A and IIF (r = 0.56, P = 0.043). It is concluded that the capture PR3- ANCA ELISA is more sensitive than PR3-ANCA ELISA, and that the capture ELISA can be used for screening of PR3-ANCA.