Tissue factor, the main initiator of blood coagulation, is released into the bloodstream when vessel damage occurs. Vessel damage may occur in ankylosing spondylitis (AS).

To measure tissue factor levels in patients with AS and to look for correlations between tissue factor levels and established clinical and laboratory markers for disease activity.

We compared patients who met modified New York criteria for AS to healthy untreated controls. Serum tissue factor was assayed using an ELISA. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), and Bath Ankylosing Spondylitis Global Score (BAS-G) were recorded, as well as the erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, and IgA level. ANOVA and t-tests were performed. P values<0.05 were considered significant.

We included 28 patients with AS (mean age, 42 years; and mean disease duration, 14 years), who had never received immunomodulating or vascular medications, and 22 same-age healthy controls. In the patients, tissue factor levels were significantly higher (32.6±33.6 vs. 9.5±11.5 pg/ml, P=0.003); they correlated with the ESR (P=0.018), CRP (P<0.0001), and IgA (P=0.023), but not with the clinical variables (BASDAI, BASFI, and BAS-G; P>0.05).

In this preliminary study in patients with AS, tissue factor levels were high and correlated with laboratory tests for inflammation. Tissue factor elevation may be a cause or a consequence of AS inflammation that promotes the occurrence of vascular events.