CONTROL OF ORAL ANTICOAGULATION IN PATIENTS WITH THE ANTIPHOSPHOLIPIDSYNDROME - INFLUENCE OF THE LUPUS ANTICOAGULANT ON INTERNATIONAL NORMALIZED RATIO

The recommended therapeutic range of International Normalized Ratio (I NR) for oral anticoagulant treatment in patients with the antiphosphol ipid syndrome remains controversial. As a part of this controversy, it has been suggested that lupus anticoagulants (LA) could interfere wit h the determination of prothrombin time, thus questioning the validity of monitoring the treatment of these patients using INR. To clarify t his point, we compared the values of INR obtained in the plasmas of tw o groups of patients, one without LA (n = 47), and the other with LA ( n = 43). INR were determined using 8 different thromboplastin reagents on the same automated coagulation instrument. Chromogenic factor X, w hich is supposed to be insensitive to the presence of LA, was also mea sured. The results are the following: provided INR was calculated usin g calibrated reference plasmas, there was no significant difference be tween INR values obtained with the 8 reagents, both in the non-LA and in the LA groups (CV: 5.9 and 6.7%, respectively). Closer examination revealed that INR results obtained with one reagent (the recombinant t hromboplastin Innovin) diverged from those of the 7 others, leading to an overestimation of INR, to a very large extent in some instances. H owever this effect was restricted to a subset of the patient populatio n with LA (6 out of 43). Finally, the relationship between INR (averag e value obtained using the 8 reagents) and factor X was identical in n on-LA and in LA patient groups. We conclude that, provided the reagent s which display the LA interference are identified and excluded for th is purpose, the INR system is valid for monitoring oral anticoagulant treatment in patients with LA.