Background suPAR is a biomarker increasingly used for the monitoring of systemic inflammation. Activation of the immune system leads to elevated serum suPAR. We aimed to evaluate suPAR for the monitoring of inflammatory activity in different rheumatic diseases including rheumatoid arthritritis (RA), systemic lupus erythematosus (SLE) and anklyosing spondylitis (AS).
Methods Serum suPAR, CRP and ESR were measured in 120 RA, 89 SLE and 33 AS patients with various disease activity and in healthy age-matched controls.
Results suPAR, CRP and ESR were higher in RA patients than in controls (4.24 [3.19-5.40] vs 2.80 [2.06-3.42] ng/mL 4.00 [0-9.83] vs 2.70 [0-4.15] mg/L and 21 [12-36.5] vs 10 [7-14] mm/h respectively p<0.04 for all, median [quartile]). When suPAR were analyzed according to DAS28, suPAR in the subgroup with DAS28<2.6 was lower than in the subgroup with DAS28>2.6, but still higher than in controls (4.45 [3.33-5.56] vs 3.66 [3.10-4.67] vs 2.80 [2.06-3.42] ng/mL p<0.0001). We further analyzed the correlation between the number of tender and/or swollen joints (TJ/SJ) and suPAR with DAS28<2.6: CRP and ESR were in the normal range but suPAR were significantly higher in patients in remission with 4 TJ/SJ than with 2-3/0-1 TJ/SJ (7.04 [6.37-11.23] vs 4.33 [3.93-4.50] vs 3.04 [2.60-3.32] ng/mL p<0.0001). suPAR and ESR were higher in SLE than in controls, while CRP were comparable. We also performed suPAR on several SLE subgroups according to various organ involvements, serological parameters and medication. suPAR in SLE with vasculitis in the history were higher than in patients without vasculitis (5.84 [4.12-7.01] vs 4.21 [3.57-5.47] p=0.04). Patients who needed to receive intravenous corticosteroid treatment during their disease had higher suPAR than patients who did not (5.37 [4.04-7.22] vs 4.09 [3.57-5.08] p=0.04. Patients with a SLEDAI of 0 were considered to be in remission, between 1-8 was regarded as low, a SLEDAI >8 was regarded as high disease activity. In case of CRP and ESR, no difference was detected according to SLEDAI. However, suPAR in patients with SLEDAI>8, were higher than in patients with SLEDAI 1-8 or 0. CRP and ESR were higher in AS patients than in controls, while suPAR were comparable (2.97 [2.57-3.80] vs 2.80 [2.06-3.42] ng/mL p>0.05). In AS patients, a correlation was detected between BASDAI indices and CRP as well as ESR but not suPAR.
Conclusions While the normalisation of CRP and ESR values suggest remission of the chronic inflammatory process in RA, suPAR values are still elevated compared to controls. suPAR is a sensitive and stable marker of inflammation in the monitoring of RA patients. It is especially valuable in the recognition of inflammatory activity in patients who are in remission according to DAS28 scores but have symptoms of TJ/SJ. While CRP and ESR values showed no differences according to SLEDAI, suPARs correlated with higher SLEDAI. Therefore, the monitoring of suPAR might be a useful tool for the follow-up of patients with mild symptoms but ongoing chronic inflammation in RA and a useful, objective marker for higher disease activity in SLE. Unlike plasma suPAR levels do not reflect inflammation in AS.
Disclosure of Interest None Declared
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