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OBJECTIVE: To investigate serum levels of calprotectin (S100A8/S100A9) and S100A12 as markers of disease activity or distinct clinical or radiographic features in patients with psoriatic arthritis (PsA). METHODS: Serum levels of calprotectin and S100A12, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) were determined in 119 patients with PsA. Correlations to clinical variables were calculated, and subgroups of patients were compared. RESULTS: The correlations to clinical disease activity measures were stronger for CRP than for ESR and calprotectin. In the regression analysis, calprotectin was identified as an independently associated factor for presence of peripheral radiographic features of arthritis (OR 1.33, 95% CI 1.01-1.76). S100A12 levels were also elevated in those with peripheral radiographic features (p = 0.036), but did not correlate with clinical variables of disease activity. CONCLUSION: Calprotectin and S100A12 do not perform better than traditional biomarkers of disease activity in PsA, but were associated with presence of peripheral radiographic features in this cross-sectional study. The patients' low level of disease activity may have led to underestimation of the associations between any biomarker and disease measures.