TFPI contributes significantly to the inhibition of Xa in vivo, despite being present at concentrations of only 2.5 nM.

The gene for TFPI is located on chromosome 2q31-q32.1, and has nine exons which span 70 kb.

A similar gene, termed TFPI2, has been identified on chromosome 7, at locus 7q21.3; in addition to TFPI activity, its product also has retinal pigment epithelial cell growth-promoting properties.

TFPI has a relative molecular mass of 34,000 to 40,000 depending on the degree of proteolysis of the C-terminal region.

TFPI consists of a highly negatively charged amino-terminus, three tandemly linked Kunitz domains, and a highly positively charged carboxy-terminus.