Optimal monitoring/management of pseudoan- eurysms associated with dissection needs further study. 5.8. Hypercoagulable States 5.8.1. Hematologic Traits Recommendation for Hematologic Traits Referenced studies that support the recommendation are summarized in online Data Supplement 45. COR LOE Recommendation In patients with ischemic stroke or TIA of unknown source despite thorough diagnostic evaluation and no other thrombotic history who are found to have prothrombin 20210A mutation, activated protein C resistance, elevated factor VIII levels, or deficiencies of protein C, protein S, or antithrombin III, anti- platelet therapy is reasonable to reduce the risk of recurrent stroke or TIA.600 606 Synopsis Hypercoagulable states refer to heterogeneous hema- tologic traits that predispose to venous or arterial thrombosis, which then may increase the risk of stroke, particularly in younger populations. Hypercoagula- ble states may increase the risk of stroke via various mechanisms. Hypercoagulable disorders may predis- pose to arterial or venous thrombosis. Among people with venous thrombosis, stroke may be caused by paradoxical emboli via right-to-left arterial shunt, either pulmonary or cardiac (often via a PFO). Hypercoagu- lable states that cause arterial thrombosis may cause stroke via distant thrombosis (eg, intracardiac) with embolization or via in situ thrombosis of the brain or cervical arteries. Suspicion for hypercoagulable states as the cause of stroke varies by clinical scenario, but they may be considered in younger populations with no identifiable cause for stroke, self- or family history of unprovoked thrombosis, prior spontaneous abortion, or coexistence of systemic signs and symptoms sugges- tive of hypercoagulability. Recommendation-Specific Supportive Text 1. 