Apparent Direct Thrombin Inhibitor (DTI) Resistance in a Patient With ...

Hematopathology 113 Id: 2LPA Apparent Direct Thrombin Inhibitor (DTI) Resistance in a Patient With Elevated Factor VIII levels Deepu Alex, Medstar-Georgetown University Hospital, Children's National Health System, Washington, DC We report a case in which there was a lack of activated partial thromboplastin time (aPTT) correlation with direct thrombin inhibitor (DTI) dosage in a patient diagnosed with May-Thurner syndrome. This is the second reported case in the literature where an apparent resistance to a DTI was associated with increased coagulation factor VIII levels. Increased factor VIII level may lead to aPTT shortening which results in apparent lack of response to DTIs. This may prompt the clinician to increase dosage which may then lead to life-threatening bleeding complications. Factor VIII level measurement in the presence of DTIs gives rise to erroneously low measurements because the endpoint of the aPTT is inhibited by the DTI as seen in this case. Thus, a chromogenic factor VIII assay would be the most accurate test to definitively ascertain the cause for the aPTT inhibition. In view of the fact that aPTT levels did not help in this clinical setting, we discuss other methods by which dosage of direct thrombin inhibitors can be monitored. These include diluted thrombin time (dTT), ecarin clotting time (ECT), and ecarin chromogenic assay (ECA). ©American Society for Clinical Pathology

Am J Clin Pathol 2014;142:A113