ANCA titres, even of IgG subclasses, and soluble CD14 fail to predict relapses in patients with ANCA‐associated vasculitis

Background. Antineutrophil cytoplasmic autoantibodies (ANCA) are presumed to reflect disease-activity and to be useful for guidance of immunosuppressive therapy of ANCA-associated systemic vasculitis (AASV), but with respect to conventional ANCA assays this is controversial. ANCA titres, measured in the IgG3 subclass and modern capture ELISAs, have been said to be superior predictors of relapses of AASV. Methods. In this retrospective study serial measurements of ANCA parameters and soluble CD14 (sCD14) were performed in 169 consecutive sera over a median of 21 months in 18 patients with AASV and related to disease activity, assessed by Birmingham Vasculitis Activity Score (BVAS) for new or deteriorated (BVASI), and for chronic disease activity (BVAS2). Fourteen patients had Wegener's granulomatosis (WG) and were C-ANCA positive with Pr 3-antibodies and four patients had microscopic polyangiitis (MPA) with P-ANCA and MPO-antibodies. In WG patients ANCA by IIF, Pr 3-ELISA for IgG, IgG1, IgG3, IgG4 and sCD14 were measured, as well as capture ELISA for Pr 3, and in MPA patients ANCA by IIF, MPO-ELISA for IgG and IgGI, IgG3, IgG4, and sCD14 respectively. In eight patients, data collection started at diagnosis, in 10 patients at remission. Results. The parameters predicted neither the nine major relapses (increase of immunosuppression necessary), nor the 26 minor relapses (increase of BVAS 1 > 2) with sufficient sensitivity ( > 80%) or specificity ( > 90%), and they also failed to predict relapses within the following 2 months. ANCA-IgG3 and capture ELISA for Pr 3 were not advantageous for prediction of relapses (sensitivity 0.45 and 0.19 respectively), and sCD14 remained elevated in all samples irrespective of disease activity. Conclusions. There is no rationale for serial measurements of ANCA in AASV. For changes of therapy, the ANCA parameters should only be used in conjunction with clinical information.