✅ An elevated prothrombin time (PT) and activated partial thromboplastin time (aPTT) indicate a deficiency of, or inhibitor against, a clotting factor in the common pathway (factor X [FX] or factor V [FV]) or combined deficiencies/inhibitors in the intrinsic and extrinsic pathways.
✅ Correction of a prolonged PT and aPTT with normal plasma (mixing study) normally suggests a deficiency in a clotting factor(s) rather than an inhibitor. However, in the case of FV, clearance-enhancing antibodies may result in autoimmune-mediated FV deficiency with a normal mixing study (i.e., one that corrects with addition of normal plasma).
✅ There is no FV concentrate available. Thus, hemostatic treatment of FV deficiency – whether inherited or acquired – requires the use of fresh frozen plasma (which has the risk of fluid overload) and platelet transfusions (because platelets carry FV).
✅ Like acquired hemophilia A (acquired inhibitor against FVIII), treatment of acquired FV deficiency that is presumed to be caused by an inhibitor includes eradication strategies such as high dose corticosteroids +/- cyclophosphamide or rituximab.