Plasma soluble urokinase plasminogen activator receptor (suPAR) levels in ankylosing spondylitis

Recent studies demonstrated that soluble urokinase plasminogen activator receptor (suPAR) is a valuable marker in the recognition of an inflammatory response. Ongoing inflammation leads to elevated plasma suPAR levels. We aimed to characterize plasma suPAR levels in ankylosing spondylitis (AS) patients compared to healthy individuals in order to reveal if suPAR could be used as a clinical marker of inflammation in AS. We measured plasma suPAR and C-reactive protein (CRP) levels as well as erythrocyte sedimentation rate (ESR) in 33 AS patients at various stages of disease duration and activity and 29 healthy controls. CRP and ESR values were higher in AS patients than in healthy individuals, while suPAR values were comparable (median [interquartile range]: 2.97 [2.57-3.80] ng/mL vs. 2.80 [2.06-3.42] ng/mL, P>0.05). In AS patients, a correlation was detected between BASDAI scores and CRP as well as ESR values but not suPAR levels (P=0.0005, r=0.57 and P=0.01, r=0.43, respectively). Unlike in many other inflammatory conditions, plasma suPAR levels do not reflect inflammation in AS. To assess the inflammatory status in AS, ESR and particularly CRP values are still more appropriate clinical markers. In line with earlier findings, our results indicate that, unlike suPAR, both of these markers are positively correlated with disease activity in AS.