The Determination of Factor X Using an Automated Amidolytic Technique

An automated method for the determination of factor X has been developed using a procoagulant fraction from Russell’s Viper Venom (RW), which activates FX within 4 minutes at pH 8.6, resulting in a Xa activity that is assayed using the chromogenic substrate S 2222. The amidolytic activity generated by sufficient RW is proportional to the FX level of the plasma and is not influenced by antithrombin III within the time studied. By using polybrene, the influence of heparin (up to 10 U/ml) can be eliminated. The method has been adapted for performance automatically on an Automated Kinetic Enzyme and Substrate analyser (Vitatron), Comparison of FX activities of 30 normals and 41 patients with bleeding disorders revealed a close correlation of this method with the one stage clotting assay using thromboplastin (r=0.93). Values obtained in a group of 83 patients on oral anticoagulant therapy showed good correlation (r=0.87) but tended to be about 8% higher compared to the one stage method. No significant differences were found when RW was used in the clotting assay (r-0.91). The values obtained by the amidolytic assay correlated well with thrombotest (r=0.87).