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 .