The present disclosure provides antibodies that selectively binds to specific forms of clotting factors, in particular, antibodies that specifically binds to activated factor IX (FIXa) wherein the anti-FIXa antibody or an antigen binding portion thereof preferentially binds to FIXa in the presence of FIXa and factor IX zymogen (FIXz), and antibodies that specifically bind to factor X zymogen (FXz) wherein the anti-FXz antibody or antigen binding portion thereof preferentially binds to FXz in the presence of FXz and activated factor X (FXa). Also provided are bispecific molecules (e.g.,antibodies) comprising,e.g.,an anti-FIXa antibody or antigen binding portion thereof and/or an anti-FXz antibody or antigen binding portion thereof. The disclosure also provides compositions encoding the disclosed antibodies and bispecific molecules, vectors, cells, pharmaceutical and diagnostic compositions, kits, methods of manufacture, methods of use, and immunoconjugates.本發明提供選擇性結合至凝血因子之特定形式的抗體,詳言之,特異性結合至活化因子IX (FIXa)之抗體,其中該抗FIXa抗體或其抗原結合部分在FIXa及因子IX酶原(FIXz)存在下優先結合至FIXa;及特異性結合至因子X酶原(FXz)之抗體,其中該抗FXz抗體或其抗原結合部分在FXz及活化因子X (FXa)存在下優先結合至FXz。亦提供包含例如抗FIXa抗體或其抗原結合部分及/或抗FXz抗體或其抗原結合部分之雙特異性分子(例如抗體)。本發明亦提供編碼所揭示之抗體及雙特異性分子之組成物、載體、細胞、醫藥組成物及診斷組成物、套組、製造方法、使用方法以及免疫偶聯物。(無)