Serum levels of the soluble urokinase plasminogen activator receptor (suPAR) correlates with disease activity in early rheumatoid arthritis and reflects joint damage over time.

Soluble urokinase plasminogen activator receptor (suPAR) is intensively studied as a biomarker of inflammation and disease outcome in various diseases. In rheumatoid arthritis (RA), suPAR have shown an association with inflammation and swollen joints, but data on suPAR in relation to early disease course and disease progression are lacking. This study investigates the potential of suPAR to predict or reflect disease outcome in early RA. Serum suPAR was measured by enzyme-linked immunosorbent assay at disease onset and after 3 and 36 months in 252 patients from a Swedish prospective observational early RA cohort. Levels and changes of suPAR were analyzed in relation to the 28-joint disease activity score (DAS28) and joint damage according to the Larsen score at inclusion and during follow-up. 100 healthy blood donors served as controls. Circulating levels of suPAR were higher in RA patients at all time points as compared to healthy controls. Baseline suPAR was significantly associated with baseline disease activity whereas suPAR levels at 36 months were associated with joint damage at 36 months. No predictive value of suPAR levels or changes in suPAR levels over time were found. In conclusion, suPAR levels associate with disease activity in early untreated RA and reflects joint damage at later stages. Increased suPAR in established RA could indicate patients in need of frequent monitoring of joint status, irrespective of disease activity. In the view of suPAR as a rapidly emerging biomarker, it is important to be aware of its ability to reflect both inflammation and subsequent damage.