Systemic lupus erythematosus (SLE) resembles rheumatoid arthritis (RA) in at least two areas: it involves joints (arthritis) and it can lead to rheumatoid factor (RF) and anti-cyclic citrullinated peptide antibodies (anti-CCP) positivity, both with a lower prevalence than in RA.
Objectives: The present study aimed to quantify the prevalence of RF and anti-CCP antibodies in a SLE group, to note their possible correlations with clinical and laboratory variables.
Materials and methods: The study analyzed 45 SLE patients, 139 RA patients and 147 normal subjects by measuring RF and anti-CCP2 titers and comparing/correlating inter-groups or subgroups divided by criteria such as arthritis and RF/anti-CCP positivity.
Results: In the SLE group, 6.7% (3/45) were anti-CCP positive, 15.5% (7/45) were RF positive and 4.4% (2/45) were positive for both tests. A cut-off titer of anti-CCP antibodies < 1.25 U/mL had 82.2% sensitivity and 90.6% specificity for SLE. A cut-off titer of RF antibodies < 18.5 U/mL had 84.4% sensitivity and 83.5% specificity for SLE. The arthritis SLE subgroup did not differ significantly from the non-arthritis SLE subgroup. Anti-CCP positive SLE patients with or without arthritis had a RF titer 6 times higher than anti-CCP negative SLE patients.
Conclusions: Anti-CCP antibodies and RF are detectable in SLE with lower titers and prevalence than in RA. The SLE articular involvement does not influence the titers and positivity frequencies of RF and anti-CCP antibodies, nor does the latter associate with SLE arthritis, suggesting no pathogenic role in the development of SLE arthritis.