title: Mechanized amidolytic technique for determination of factor X and factor-X antigen, and its application to patients being treated with oral anticoagulants.
abstract: We describe a mechanized chromogenic assay for factor X, the results of which correlate well with those for the one-stage clotting assays for factor X in which it is activated either via the extrinsic pathway by thromboplastin or directly by Russell's viper venom. We purified human factor X and raised monospecific antibodies to it in rabbits. We used our chromogenic assay for factor X to develop a factor-X-inhibitor neutralization assay for determination of factor-X antigen. Patients receiving oral anticoagulant treatment had significantly different factor-X activities after activation via thromboplastin or with Russell's viper venom. The concentration of factor-X antigen, although decreased, significantly exceeded factor-X clotting activity or chromogenic activity in this group of patients. Results of the chromogenic assay for factor X correlated well with results of "Thrombotest," a clotting test introduced by Owren (Lancet ii: 754, 1959) to control anticoagulant therapy. For patients taking oral anticoagulant drugs, the therapeutic range by our assay is 180 to 300 units/L.
mesh_terms: D000925:Anticoagulants / Q000627:therapeutic use*; D000941:Antigens / Q000032:analysis*; D001322:Autoanalysis; D001780:Blood Coagulation Tests; D005170:Factor X / Q000032:analysis* / Q000276:immunology / Q000302:isolation & purification; D005171:Factor X Deficiency / Q000097:blood*; D006801:Humans; D007020:Hypoprothrombinemias / Q000097:blood*; D013925:Thromboplastin; D014757:Viper Venoms
chemical_list: D000925:Anticoagulants; D000941:Antigens; D014757:Viper Venoms; D005170:Factor X; D013925:Thromboplastin