Vitamin K antagonists (1,2) are employed in oral anticoagulant therapy for the prevention of thromboembolic disorders in patients at risk (3). These drugs inhibit the regular hepatic synthesis of the vitamin K dependent blood clotting proteins, e.g. prothrombin, factor VII, factor IX and factor X, by blocking the availability of the proper form of vitamin K for participation as a cofactor in the post-translational modification of glutamic acid to gamma-carboxyglutamic acid. gamma-carboxyglutamic acid is required in these proteins to permit calcium dependent protein-membrane interaction and full biologic activity (4). Decreased activities of the vitamin K dependent coagulation factors II, VII, IX and X lead to therapeutically used reduced blood clottability, which also causes a prolongation in the in vitro blood clotting test prothrombin time PT (5). The degree of PT prolongation represents the in vivo reduction of hemostatic competence. The simplicity of performance and the good correlation with the in vivo hemostatic situation make this test a useful tool for monitoring the intensity of treatment with oral anticoagulants. Because of the low toxic-therapeutic ratio, the risk of bleeding associated with vitamin K antagonist therapy is highest in patients who are not carefully monitored. As regular PT testing is required in these patients, test systems using capillary blood (6) have been introduced in order to accelerate analysis and to avoid frequent venipunctures. In the present study the conventional method used in our hospital, THROMBOTEST(R) reagent on KC-1 instrument, was compared with the newly developed COAGUCHEK(R) method.
