Which of the following statements is false about unfractionated heparin?

Heparins act by activating anti-thrombin III (not inhibition) Unfractionated heparin acts by activating antithrombin III (AT III) in plasma. Normally AT III inactivates several clotting factors, most impoantly factor Xa and IIa (thrombin) but the reaction is very slow. Heparin accelerates this inactivation process by binding to ATIII and inducing the conformational change in it to expose the binding sites. Only conformational change is required for inactivation of factor Xa whereas inactivation of thrombin is also dependent on formation of scaffolding by heparin (that binds both ATIII and IIa). Unfractionated heparin provides this scaffolding and thus inhibits both factor IIa and Xa whereas LMW heparins and fondaparinux only cause conformational change in ATIII and thus inhibit only factor Xa. As heparin inhibits already activated factors, so there is no time lag between the administration and action of this drug, therefore it can be used both in vivo as well as in vitro.