Factor XI Levels in Acute Ischemic Stroke
Factor XI Levels in Acute Ischemic Stroke
The purpose of this study is to evaluate the utility of measuring coagulation factor
 activities in the setting of acute ischemic stroke, as potential markers of inherited
 thrombotic risk. The investigators will determine if relationships exist between coagulation
 factors, including factor VIII, factor IX, and factor XI and clinical diagnosis,
 classification, and outcome. The investigators will determine if any significant elevations
 of these factor activities are independent thrombotic risk factors.

 Null Hypothesis: There is no statistical difference between coagulation factors, including
 factors VIII, IX, or XI activity levels in patients having acute ischemic stroke as compared
 to acute stroke mimics.
Increased factor XI levels have been associated with venous thromboembolic disease and acute
 myocardial infarction. However, checking factor XI levels is not currently indicated to
 assess individual thromboembolic risk. Factor XI is an important protease that links the
 extrinsic arm of the coagulation cascade with the intrinsic arm through dual activation by
 both factor XII and thrombin. Since thrombin is a downstream product of factor XI, a feedback
 loop is created that amplifies thrombin production and ultimately results formation of a
 stable fibrin clot. Sufficient thrombin generation via this pathway also contributes to
 activation of the Thrombin-Activatable Fibrinolysis Inhibitor (TAFI). Activated TAFI
 downregulates fibrinolysis and has been implicated as part of the association between
 elevated factor XI levels and venous thromboembolic disease. One study found that functional
 TAFI levels of > 120% increased the risk of ischemic stroke approximately 6-fold, however,
 the association between Factor XI and ischemic stroke has yet to be firmly established. We
 recently performed a preliminary retrospective analysis of 78 patients with stroke or
 transient ischemic attack (TIA) and found that patients with factor XI activity levels above
 the 95th percentile of an age and sex matched reference population had a relative risk of 5.3
 for stroke or TIA. Factor XI measurements may be able to help identify thromboembolic
 disease, aiding in the determination of stroke etiology.
Inclusion Criteria:

 -  Those clinically diagnosed with acute ischemic stroke

 -  18 years of age or greater

 Exclusion Criteria:

 -  Those without clinical diagnosis of acute ischemic stroke will be included in the
 control group.

 -  Patients with hemorrhagic strokes

 -  Inpatients who are evaluated through the Brain Attack protocol