There are two functional assays. The amount of activated factor X generated is inversely proportional to the amount of TFPI present. The modified PT is not as complex but requires the use of anti- TFPI antibodies. A prothrombin time is performed on plasma with and without added anti-TFPI antibodies. The difference in times is proportional to the amount of TFPI present.
Diluted plasma is incubated in a test well precoated with the initial capture antibody.
This second antibody has horseradish peroxidase enzyme attached. After washing, to remove unbound indicator antibody, an appropriate substrate is added and the amount of color produced is proportional to the amount of TFPI present. It may well be that tests for these anticoagulants will never be sensitive and accurate enough for routine use. Even if they are, the fact still remains that trying to identify potential clotters would require an extensive, ongoing screening program. This, as we all know, is not financially feasible.