Plasma samples from the patients with VTE were obtained from Dr. Anetta Undas (Institute of Cardiology, Jagiellonian University, Kraków, Poland). Cellular Fn-EDA levels in the plasma were measured by sandwich enzyme-linked immunosorbent assay (ELISA) as described.[14 (link)–16 (link)] Briefly, microtiter plates were coated overnight at 4°C with primary antibody for Fn-EDA (3E2, 10 μg/mL, Sigma, catalog # F6140) diluted in 50 mM sodium carbonate buffer. 10 μl of plasma samples (diluted 1:1 in PBS) were incubated for 2 h in the coated wells at 37°C. After five washes, biotinylated secondary antibody to Fn (2 μg/ml diluted in blocking buffer, Sigma, catalog # F3648) was added to wells and incubated for 1 hour at room temperature. The avidin HRP solution (1:1000) in the blocking buffer was added to wells and incubated for 30 minutes following five washes. Micro titer plates were washed five times before adding 3, 3’, 5, 5’-tetramethylbenzidine substrate solution (Sigma, catalog # T0440) to the wells, and the colorimetric reaction was stopped with 2 M H2SO4 after 10 min. Results were read in an ELISA microplate reader at A450 nm. Human cellular Fn (Sigma, catalog # F2518) was used for standards.