It has been suggested that lupus anticoagulants (LA) could interfere not only with clinical course of the oral anticoagulant treatment but also with determination of prothrombin time. Thus question of the validity of monitoring warfarin treatment using INR arises in patients with antiphospholipid syndrome. To clarify this point, we compared the values of INR obtained in the plasmas of two groups of patients on oral anticoagulant treatment; one with LA and the other one without LA, during one year period. We could not prove any differences comparing clinical course, relative number of INR values under or over target therapeutic interval and number of the days in the target therapeutic range between these two groups of the patients.

        Key words: lupus anticoagulant, anticoagulant treatment, prothrombin time