A CLINICAL-STUDY MONITORING LOW-INTENSITY ANTICOAGULANT-THERAPY WITH A STANDARD-SENSITIVITY THROMBOPLASTIN

The ability of the prothrombin time to measure the anticoagulant effec t of warfarin sodium varies depending on the particular tissue thrombo plastin used in performing the test. Based on studies using sensitive thromboplastins, lower therapeutic ranges of anticoagulation are recom mended. The adequacy of monitoring therapy in this lower range with th e relatively insensitive thromboplastins commonly used in North Americ a is unestablished. This 16-month prospective study used a standard No rth American thromboplastin to monitor 157 anticoagulated patients tre ated in a low therapeutic range. Of the 1734 prothrombin times generat ed, 876 (56%) were therapeutic, with 400 (23%) below and 458 (26%) abo ve the therapeutic range. These results are comparable with those publ ished in trials in which more sensitive thromboplastins were used in a similar therapeutic range. We conclude that standard North American t hromboplastins are adequately suited to monitor therapy in this lower range.