Immundiagnostischer stellenwert der antigenspezifischen ELISAs in der ANCA-diagnostik bei primaren systemischen vaskulitiden

The indirect immunofluorescence test (IFT) is used as a screening method for anti-neutrophil cytoplasmic antibodies (ANCA) as diagnostic markers for systemic vasculitides. The sensitivity and specificity of ANCA antigen detection (proteinase 3 (PR3) and myeloperoxidase (MPO)) by ELISA differs considerably between centers. We assessed commercial ELISA kits in respect to their specificity and sensitivity in detecting PR3-ANCA (7 kits) and MPO-ANCA (8 kits) and their correlation with the IFT results. Sera from 5 patients with systemic lupus erythematodes (SLE), 28 with Wegener's granulomatosis (WG), 22 with microscopic polyangiitis (MPA), 5 with idiopathic rapidly progressive glomerulonephritis (RPGN), and 5 healthy controls were examined by IFT and commercial ELISA kits. Sera from healthy controls, patients with SLE and cANCA-negative WG were shown to be PR3-ANCA-negative by all 7 PR3- ANCA kits. In 25 cANCA-positive sera from WG patients, PR3-ANCA positivity ranges from 44% to 84%. The PR3-ANCA levels in 5 of 7 kits correlated with the cANCA titers in IFT. Sera from healthy controls, 4/5 SLE and all pANCA- negative SLE patients were found to be MPO-ANCA-negative in all 8 MPO-ANCA kits. In 20 pANCA-positive sera, MPO positivity ranged from 25% to 75%. Only 35% of the MPO-ANCA-positive sera could be confirmed by other immunological methods. No significant correlation was observed between pANCA titers and MPO-ANCA levels. The PR3 and MPO-ANCA ELISA kits under investigation show a great variability concerning their sensitivity and in case of MPO concerning their specificity, too. So far, the method of choice for ANCA screening remains the IFT.