CD40LG and rheumatoid arthritis: Since IgM rheumatoid factor (RF) could also be a confounding factor, we compared RF levels between the patients who displayed ACPA IgM ≥ 100 AU/ml with those who had ACPA IgM < 100 AU/ml and observed that in RA patients with ACPA IgM ≥ 100 AU/ml, the levels of RF IgM were higher than in RA patients who had ACPA IgM < 100 AU/ml (RF IgM 50 AU/ml (25 to 118) and 28 AU/ml (12 to 60), respectively).