there's a big mystery about factor XII
because being on the top of the intrinsic pathway one should expect real hemorrhagic tendency when it's deficient, however the most common clinical presentation is simple incidental high PTT
but it is also plasminogen activator therefore it's needed to dissolve the clot and it's deficiency has been proposed as a cause of thrombosis
I think the latter effect is more loved by USMLE question makers
So you pick thrombosis
