Clinical and laboratory pattern of patients with systemic lupus erythematosus seropositive for rheumatoid factor.

Introduction: The aim of the study was to investigate the associations between the presence and level of rheumatoid factor (RF) in the blood serum and the clinical and laboratory characteristics of patients with systemic lupus erythematosus (SLE).

Material and methods: This retrospective tricentric cross-sectional study analyzed a Ukrainian contingent of SLE patients. Medical records of 495 patients were evaluated. Rheumatoid factor serum concentration was tested in 206 of them (41.6%) using turbidimetry technique. Clinical manifestations, routine laboratory parameters, specific immunological tests, disease activity (SLEDAI-2K), and damage indices (SLICC/ACR DI) were evaluated.

Results: Our study revealed that RF was elevated in 27.7% of patients. The RF-positive patients experienced a longer delay in SLE diagnosis (2.0 vs. 0.5 years, p = 0.046), less frequent kidney involvement (42.1% vs. 59.4%, p = 0.045) and fever (42.1% vs. 59.2%, p = 0.046), and more frequent lymphadenopathy (59.6% vs. 42.3%, p = 0.039) compared to RF-negative patients. Patients with RF positivity had higher levels of C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and antinuclear antibody (ANA) titer, and were more frequently positive for antibodies to Ro/SSA and La/SSB. Rheumatoid factor concentration directly correlated with CRP (r = 0.318; p < 0.01) and ESR (r = 0.228; p = 0.04) levels. However, no associations were found between RF levels and SLEDAI-2K, joint involvement frequency, SLICC/ACR DI or drug therapy content. Univariate logistic regression analysis showed that RF positivity was independently associated with lymphadenopathy, presence of anti-Ro/SSA and anti-La/SSB antibodies, and negatively associated with kidney involvement.

Conclusions: In RF-seropositive SLE patients (approximately 28%), the diagnosis is established later compared to RF-seronegative ones; kidney involvement and fever are less common, while lymphadenopathy develops more frequently. Rheumatoid factor seropositivity is associated with higher levels of ESR, CRP, ANA, and the presence of antibodies to Ro/SSA and La/SSB. According to the results of univariate logistic regression analysis, an independent association with RF positivity was confirmed only for kidney involvement, lymphadenopathy, and antibodies to Ro/SSA and La/SSB.