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

• Dotblot and Phadia EliA are rapid testmethods for ANCA and anti-GBM determination.
• Both testmethods have excellent performance in acute severe disease manifestations of suspected small-vessel vasculitis.
• Learning points/highlights: Urgent serological testmethods have a important role in diagnosis of life-threatening small-vessel vasculitis.

BackgroundIn 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.ObjectiveWe analysed the diagnostic performance of two rapid ANCA and anti-GBM test methods in 260 patients with suspected AAV.MethodsBetween 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.ResultsSeventy-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-PR3s or anti-MPOs 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%).ConclusionThe Dotblot and Phadia ELiA on anti-GBM, anti-PR3s and anti-MPOs 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.