Further evaluation of an automated amidolytic factor X assay in monitoring anti-vitamin K treatment.

A mechanized factor X assay was tested in 2222 plasma samples of patients being treated with oral anticoagulants. The correlation coefficient between this assay and Thrombotest was 0.78. The therapeutic range for factor X amidolytic activity was 150 to 300 units/l. Amidolytic factor X activity and Thrombotest provide similar information about the state of anticoagulation within the same patient, including patients that are not well balanced. The ranges for factors II, VII, IX and X clotting activity in 57 patients on long-term therapy (Thrombotest within the therapeutic range between 190 and 95 s) were 80-300, 70-600, 40-420 and 50-330 units/l, respectively. The range for factor X amidolytic activity in this group of patients was 150-470 units/l.