PRTN3 and rheumatoid arthritis: In contrast, within the ACPA– RA subgroup, we identified fourteen metabolites, including biliverdin, bilirubin (Z,Z), and a bilirubin degradation product (C17H20N2O5), that demonstrated significant negative correlations (ρ < –0.4 and P < 0.05) with ESR (Figure 2F; Supplementary Table S5).