HDCN Article Review/Hyperlink

Moll S, Ortel TL

Monitoring warfarin therapy in patients with lupus anticoagulants

Ann Intern Med (Aug) 127:177-185 1997

The INR has been recommended as the most appropriate way to monitor patients on coumadin with lupus anticoagulants following thromboembolic events. Because many of these patients may already have a prolonged prothrombin time (PT), Moll and Ortel used several thromboplastins to determine the prevalence of prolonged PT's in patients with lupus anticoagulants and to determine the utility of the INR in assessment of those patients receiving coumadin. They identified 161 patients at Duke University over a three year period with lupus anticoagulants. Further investigation was performed on 34 patients using nine commercially available thromboplastins and coagulation tests that measured INR's, prothrombin-proconvertin times, chromogen factor X levels and factor II levels. While the first two assays correlated with each other, INR's varied widely (by as much as 0.4 - 6.5 in a single patient) and factor II assays overestimated anticoagulation.

This study demonstrated that the INR provides variable levels for patients with lupus anticoagulants receiving warfarin depending on the thromboplastin used. While the most reliable results were obtained using chromogenic factor X and prothrombin-proconvertin time assays, these are not readily available. The INR is particularly unreliable in patients with baseline elevated PT's. While the authors demonstrate how unreliable the INR can be in monitoring the appropriate degree of anticoagulation in these patients, no practical recommendation is offered and further study is clearly needed. (N. Kevin Krane, M.D., Tulane University School of Medicine)

The abstract of this paper is available from the National Library of Medicine's PubMed site: click here .