Human Phenotype Ontology identifier HP_0008321 (Reduced factor X activity) is reduced activity of coagulation factor X. The extrinsic and intrinsic pathways converge at factor X (fX). The extrinsic pathway activates fX by means of d factor VII with its cofactor, tissue factor. The intrinsic pathway activates fX by means of the tenase complex (Ca2+ and factors VIIIa, IXa and X) on the surface of activated platelets. Factor Xa in turn activates prothrombin (factor II) to thrombin (factor IIa). Also known as: Decreased factor x activity.