Performance of two strategies for urgent ANCA and anti-GBM analysis in vasculitis.

BACKGROUND: In anti-neutrophil cytoplasmic antibodies (ANCA) associated small vessel vasculitis (AAV), rapid testing for ANCA and anti-glomerular basement membrane (GBM) antibodies may be beneficial for therapeutic purpose. OBJECTIVE: We analysed the diagnostic performance of two rapid ANCA and anti-GBM test methods in 260 patients with suspected AAV. METHODS: Between January 2004 and November 2010, we analysed 260 samples by qualitative Dotblot (Biomedical Diagnostics); retrospective analysis followed with directly coated highly sensitive automated Phadia ELiA and ELiA anti-GBM. Results were related to the final clinical diagnosis and compared with routine capture ELISA. RESULTS: Seventy-four patients had a final diagnosis of AAV (n=62) or anti-GBM disease (n=12). Both Dotblot and ELiA detected all 12 cases of anti-GBM disease; 2 false positive results were found. Dotblot detected ANCA in 56 of 62 AAV patients (sensitivity 90%, NPV 97%), and showed 5 false positives (specificity 97%, PPV 90%). The Phadia ELiA anti-PR3(s) or anti-MPO(s) was positive in 57 of 62 AAV patients (sensitivity 92%, NPV 97%), and had 5 false positives (specificity 97%, PPV 88%). Routine capture ELISA was equally accurate (sensitivity 94%, specificity 97%, PPV 88%, NPV 98%). CONCLUSION: The Dotblot and Phadia ELiA on anti-GBM, anti-PR3(s) and anti-MPO(s) performed excellently; results were almost identical to routine ELISA. When suspicion of AAV or anti-GBM disease is high and diagnosis is urgently needed, both tests are very powerful for rapid serological diagnosis. Further studies have to confirm the test performances in samples routinely presented for ANCA testing and in follow-up of positive patients.

Recombinant protein to analyze autoantibodies to proteinase 3 in systemic vasculitis.

The presence of antineutrophil cytoplasmic autoantibodies with specificity for proteinase 3 (PR3-ANCA) usually is detected by enzyme-linked immunosorbent assay (ELISA) with purified PR3 as a substrate. We studied the technical performance of direct and capture ELISA using a recombinant proteolytically inactive form of PR3 produced in the baculovirus expression system for the detection of PR3-ANCA in 114 patients with systemic vasculitis at diagnosis. We found that ELISA using recombinant PR3 produced in insect cells is a promising alternative for ELISA with native PR3. We found a correlation between tests using recombinant or native PR3, as well as correlation of the ELISA results with ANCA titers measured by the indirect immunofluorescence technique. However, the specificity for ANCA-associated vasculitis of ELISA with recombinant PR3 was lower than ELISA using native PR3. Compared with the direct assay, capture ELISA is a more sensitive method for PR3-ANCA detection, with both native and recombinant PR3, and its results depend on the monoclonal antibody used to capture the antigen.