Chymotrypsin-like activity was higher in RA (median 23.70 nM/mg total protein, range 16.29–37.03) compared to PsA SF (median 14.55 nM/mg total protein, range 8.59–22.10, p=0.005), with OA SF levels (median 21.93 nM/mg total protein, range 11.40–29.21) not significantly different to either RA (p=0.718) or PsA SF levels (p=0.129; Figure 3B). Here, CTRL is linked to rheumatoid arthritis.