What blood test is used to determine of there is a high risk of thrombosis in the blood?

Testing platelets won't tell you anything anything in your test. They are only one part of the clotting cascade. I don't do hematology, but maybe maybe levels of prothrombin, thrombin, and fibrin might fit the bill. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1474204/ The mechanism by which OC pills can increase coagulation isn't known. Here's a summary: http://answers.yahoo.com/question/index?qid=20090707070904AAMHEBJ

Platelet count. Platelets (thrombocytes) are tiny fragments of cells called megakaryocytes that are made in the bone marrow. These fragments (about 2-3 microns in diameter) are released from the bone marrow to circulate in the blood. They are the first components to be activated when there has been an injury to a blood vessel or tissue. Because they are very "sticky," they begin the formation of a blood clot. The platelet count is a test that determines the number of platelets in your blood. Take care

Platelet count. Platelets (thrombocytes) are tiny fragments of cells called megakaryocytes that are made in the bone marrow. These fragments (about 2-3 microns in diameter) are released from the bone marrow to circulate in the blood. They are the first components to be activated when there has been an injury to a blood vessel or tissue. Because they are very "sticky," they begin the formation of a blood clot. The platelet count is a test that determines the number of platelets in your blood. Take care