Rheumatoid factor positivity in antineutrophil cytoplasmic antibody-associated vasculitis: a distinct clinical entity or innocent bystander?

Objective: To investigate the significance of RF positivity in ANCA-associated vasculitis (AAV) patients. Methods: AAV patients were divided into groups as follows: RF (+)/ANCA (+) (n = 94), RF (-)/ANCA (+) (n = 80), RF (+)/ANCA (-) (n = 15) and RF (-)/ANCA (-) (n = 25). Their clinical data, organ involvement patterns, laboratory data, and patient outcomes were assessed. Kaplan-Meier analysis and propensity score matching (PSM) were performed to compare outcomes and analyse differences between the groups. Results: Of the 214 patients, RF and ANCA positivity was found in 109 (50.9%) and 174 (81.3%) patients, respectively. RF (+)/ANCA (+) patients more frequently presented with general manifestations (58.5%) than the other groups. Additionally, compared with those of RF (-)/ANCA (+) group, RF (+)/ANCA (+) patients were older, had higher white blood cell, neutrophil, platelet counts and acute phase reactants; however, creatinine and albumin levels were lower. The end-stage kidney disease-free survival rate was significantly higher in the RF (+)/ANCA (+) group (P =0.013), while the proportion of renal involvement was comparable to the RF (-)/ANCA (+) group. PSM showed no difference in patient outcomes between the two groups after adjustment. Conclusion: RF positivity was associated with a distinct phenotype in AAV patients. In particular, difference was observed in clinical features and outcomes between RF (+)/ANCA (+) and RF (-)/ANCA (+) groups, although the direct prognostic implication of RF was not evident.