Vascular injury and endothelial cell (EC) activation are pathogenic hallmarks of systemic sclerosis (SSc; scleroderma). Human CD90 is highly expressed on activated ECs and can be shed from the cell surface. This study was conducted to examine whether soluble CD90 (sCD90) is elevated in the sera of patients with SSc and linked to pulmonary involvement and in particular, pulmonary arterial hypertension (PAH).

sCD90 serum concentrations were assessed in 76 patients with SSc and related to clinical data, lung function, 6‐minute walk distance, echocardiography, bronchoalveolar lavage fluid, and laboratory parameters. Thirty‐one healthy volunteers and 29 patients with idiopathic retroperitoneal fibrosis (IRF) served as controls.

sCD90 serum concentrations were elevated in patients with SSc compared to healthy volunteers (P = 0.001) and patients with IRF (P = 0.01). SSc patients with pulmonary fibrosis (P = 0.006) and patients with PAH (P < 0.001) had increased sCD90 serum concentrations compared to patients without the respective pulmonary manifestation of SSc. sCD90 levels correlated with diffusing capacity for carbon monoxide (n = 65; r = −0.348, P = 0.005) and systolic pulmonary artery pressure (n = 53; r = 0.469, P < 0.001). Receiver operating characteristic curve testing determined an optimal cutoff value of ≥626 ng/ml with a sensitivity of 68% and a specificity of 83% for PAH (area under the curve 0.773, 95% confidence interval 0.648–0.898; P < 0.001).

sCD90 concentrations were increased in the sera of SSc patients, particularly in patients with vascular involvement of the lungs. These data suggest that sCD90 should be further evaluated as a marker for diagnosis of PAH in SSc.