Rheumatoid factor false positivity in patients with ANCA-associated vasculitis not having medical conditions producing rheumatoid factor

We investigated the rate of rheumatoid factor (RF) false positivity at diagnosis and its influence on clinical and prognostic features and rheumatoid arthritis (RA) development during the follow-up in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) patients without RA or other medical conditions triggering RF false positivity. We reviewed the medical records of 128 AAV patients. We divided patients with AAV and each variant into two groups according to RF positivity and compared variables between the two groups. Odds ratio and cumulative relapse-free survival rate were obtained by multivariate logistic regression analysis and the Kaplan-Meier survival analysis, respectively. The mean age at diagnosis was 53.6 years and 41 patients were male. Of 128 AAV patients, 69 patients (53.9%) were classified as microscopic polyangiitis (MPA), 29 (22.7%) as granulomatosis with polyangiitis (GPA) and 30 (23.4%) as eosinophilic GPA (EGPA). The rate of RF false positivity was 39.1% in AAV patients. On univariate analysis, general, cutaneous and mucous and ocular manifestations and myeloperoxidase (MPO)-ANCA (or perinuclear (P)-ANCA) positivity were associated with RF false positivity in patients with AAV. On multivariate analysis, cutaneous manifestation was the only independent predictor of RF false positivity in EGPA patients. RF false positivity had no influence on cumulative relapse-free survival rate of AAV or RA development during the follow-up. RF false positivity rate was 39.1% in AAV patients and it was associated with cutaneous manifestation in EGPA patients at diagnosis, but not relapses of AAV or RA development during the follow-up.