the blood coagulation factors. Recent work has identified a variant (base 20210G->A) in the 3' untranslated region of the prothrombin gene that is associated with an increased risk for venous thrombosis. Approximately 20% of Dutch patients with a family history of venous thrombosis are heterozygotes for the 20210A allele, as compared to about 1% of healthy controls. In a populationbased study, the 20210A allele appears to increase the risk of venous thrombosis about 3-fold for adults of both sexes. This test determines the presence or absence of the 20210G (normal) and 20210A (variant) alleles in the prothrombin gene. PROTHROMBIN TIME Method: Clot based assay The prothrombin time (PT) is used to detect abnormalities in the extrinsic and common pathway of coagulation. Specifically, the PT is prolonged if there is a decrease in factor II, V, VII, X and/or fibrinogen. The degree of prolongation is dependent upon the severity of the deficiency and the number of clotting proteins decreased. The PT is affected by elevated factor II, V, VII and X resulting in shortening of the PT. Since each lot of thromboplastin is slightly different, reference ranges need to be determined for the specific lot used. The sensitivity of the thromboplastin to various factor levels as a single factor deficiency or combined as multiple factor deficiency is influenced by the international sensitivity index (ISI) value of the thromboplastin. Our laboratory uses a thromboplastin with an ISI value of less than 1.4. Direct thrombin inhibitors, such as argatroban and lepirudin, will falsely prolong clotting times in this assay. PROTHROMBIN TIME 1:1 MIX The prothrombin time (PT) may be prolonged due to a factor(s) deficiency or an inhibitor. A 1:1 mix is used to differentiate between the two. Equal parts of patient plasma and normal plasma pool are mixed together and a PT performed on the mixture. Correction of the patient prolonged PT on the mixture indicates a factor deficiency. Non-correction or partial correction indicates an inhibitor. PROTHROMBIN FRAGMENT 1.2 (Research test only) Method: ELISA Prothrombin fragment 1.2 is a polypeptide released from prothrombin when it is activated to thrombin by the prothrombinase complex (activated factor X and V, calcium and phospholipid). Elevated F 1.2 levels occur when prothrombin is converted in vivo at an accelerated rate and can be used as a marker for in vivo thrombin generation. Prothrombin fragment 1.2 is a quantitative marker to assess the degree to which the coagulation system has been activated. The assay has been used to assess thrombotic risk and monitor the lowest dose of warfarin needed to prevent a thrombotic event in those patients on oral anticoagulant therapy. Elevated levels are observed in inherited thrombophilia (protein C deficiency, protein S deficiency, and antithrombin deficiency). Increased levels occur in thrombosis, pulmonary embolism, DIC, trauma, septicemia and complications of pregnancy. Patients on oral anticoagulant therapy have reduced levels of F1.2. 33 THROMBIN TIME Method: Clot based assay The thrombin time will be prolonged when the fibrinogen concentration is 100 sec with heparin levels >0.05 unit/mL. The thrombin time reagent uses bovine thrombin. A patient with a prolonged thrombin time that is not due to heparin and does not correct on 1:1 mix who has recently been exposed to topical bovine thrombin should be checked for a bovine thrombin inhibitor. In the presence of this inhibitor the thrombin time will often be normal if human thrombin is used in the test system. Direct thrombin inhibitors, such as argatroban and lepirudin, will falsely prolong clotting times in this assay. THROMBIN TIME 1:1 MIX A 1:1 mix of the thrombin time is used to distinguish an inhibitor from a decreased fibrinogen level. Equal parts of patient plasma and normal plasma pool are mixed and the thrombin time repeated. Complete correction indicates a fibrinogen deficiency. No correction or only a partial correction indicates the presence of an inhibitor. tPA ACTIVITY (Tissue Plasminogen Activator Activity) Method: Immunofunctional, plasminogen-chromogen substrate (amidolytic) assay Tissue-type plasminogen