PF4 and rheumatoid arthritis: Plasma concentrations of CXCL4 were higher in AAV (112 ng/mL, p = 0.0010), SLE (54 ng/mL, p = 0.0060) and RA (48 ng/mL, p = 0.019) patients than in HCs (26 ng/mL) (Fig. 4C).