Why Direct Xa inhibitors have no effect on TT?

[zeevee]

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Please , why ?

 

[chillaxbro]

IDK but according to wiki, TT works by adding anticoagulant to blood and then adding a ton of thrombin to measure time of clot formation. I think it measures fibrinogen/fibrin activity. X is upstream of this so maybe that's why it doesnt matter

 

[aspiringmd1015]

that makes sense, bc theyre specifically checking only the 2 to 2a step, and by adding exogenous products, you wont need the upstream stuff.

 

[worldbeater]

For direct Xa inhibitors, drugs that end in "ban" are used, so you can remember it as "ban the X"

 

[worldbeater]

X is upstream of this so maybe that's why it doesnt matter

Yeah, correct, this was my thought. Intrinsic and extrinsic come together to form "X + V", and then it moves downwards to prothrombin -> thrombin, fibrinogen -> fibrin

Everything before X in the intrinsic (PTT) and extrinsic (PT) will be prolonged/"backed up".