Low frequency of elevated prothrombin times in patients with lupus anticoagulants when using a recombinant thromboplastin reagent: implications for dosing and monitoring of oral anticoagulant therapy

Many patients with lupus anticoagulants (LA) are treated with oral anticoagulation and monitored using the international normalised ratio (INR) derived from the prothrombin time (PT). Recent reports have produced conflicting conclusions about the extent to which LA interferes with PT determination. The degree of anticoagulation may be overestimated in a patient whose LA affects the PT. A number of reports conclude that specific thromboplastin reagents containing recombinant tissue factor are sensitive to the presence of LAs and should not be used to monitor oral anticoagulant therapy in these patients. These studies were performed on orally anticoagulated patients. The present retrospective study on 400 patients with LAs who were not receiving therapeutic anticoagulation was performed to ascertain the frequency of prolonged PT in these patients when using Innovin recombinant thromboplastin. Only 17 (4.3%) out of 400 had prolonged PT in the presence of LA. As this is a low prevalence, and not all patients with LAs will require anticoagulant therapy, it is concluded that baseline INR determination should be used to highlight the need to monitor individual patients with LA-insensitive reagents. As the use of moderate-intensity oral anticoagulation for patients with LAs and previous thrombosis is receiving wider acceptance, an informed approach to anticoagulant monitoring will reduce the possibility of under-anticoagulating patients receiving this therapy.