<prompt> Low molecular weight heparin affects which factor:Factor XAnti-thrombinFactor XaFactor IX  <response>: Ref: KD Tripathi, 6th Ed. pg. 597-598 Low molecular heparin inhibits factor Xa mainly, having some action at factor IIa as well. It doesnt require monitoring because of consistent bioavailability. Heparin is a powerful and instantaneously acting anticoagulant, effective both in vivo and in vitro. It acts indirectly by activating plasma antithrombin III The heparin -AT III complex then binds to clotting factors of the intrinsic and common pathways Xa, IIa, IXa, XIa, XIIa and XIIIa and inactivates them. Warfarin on the other hand is effective only in vivo body. It acts by inhibiting vitamin K.Note Fondaparinaux is synthetic LMWH acts exclusively at factor Xa. 