PRTN3 and rheumatoid arthritis: When we classified patients as seronegative (RF-negative and ACPA-negative) or seropositive (RF-positive and/or ACPA-positive), the relationship between IgG G0/G1 ratio and CRP was significantly stronger in seronegative than in seropositive RA (p < 0.0001, pBonferroni < 0.0012) (Fig. 9).