Plasminogen activator inhibitor-1, an inhibitor of fibrinolysis, is present in higher levels in people with obesity. Obese people also have larger numbers of circulating microvesicles (fragments of damaged cells) that bear tissue factor. Platelet aggregation may be increased, and there are higher levels of coagulation proteins such as von Willebrand factor, fibrinogen, factor VII and factor VIII. Obesity also increases the risk of recurrence after an initial episode of thrombosis. Unclear
A number of conditions that have been linked with venous thrombosis are possibly genetic and possibly acquired. These include: elevated levels of factor VIII, factor IX, factor XI, fibrinogen and 
thrombin-activatable fibrinolysis inhibitor, and decreased levels of tissue factor pathway inhibitor. Activated protein C resistance that is not attributable to factor V mutations is probably caused by other factors and remains a risk factor for thrombosis.There is an association between the blood levels of homocysteine and thrombosis, although this has not been reported consistently in all studies. Homocysteine levels are determined by mutations in the MTHFR and CBS genes, but also by levels of folic acid, vitamin B6 and vitamin B12, which depend on diet. Mechanism
Thrombosis is a multifactorial problem because there are often multiple reasons why a person might develop thrombosis. These risk factors may include any combination of abnormalities in the blood vessel wall, abnormalities in the blood flow (as in immobilization), and abnormalities in the consistency of the blood.
If cost-effectiveness (quality-adjusted life years in return for expenditure) is taken as a guide, it is generally unclear whether thrombophilia investigations justify the often high cost, unless the testing is restricted to selected situations.Recurrent miscarriage is an indication for thrombophilia screening, particularly antiphospholipid antibodies (anti-cardiolipin IgG and IgM, as well as lupus anticoagulant), factor V Leiden and prothrombin mutation, activated protein C resistance and a general assessment of coagulation through an investigation known as thromboelastography.Women who are planning to use oral contraceptives do not benefit from routine screening for thrombophilias, as the absolute risk of thrombotic events is low. If either the woman or a first-degree relative has had thrombosis, the risk of developing thrombosis is increased. Screening this selected group may be beneficial, but even when negative may still indicate residual risk. Professional guidelines therefore suggest that alternative forms of contraception be used rather than relying on screening.Thrombophilia screening in people with arterial thrombosis is generally regarded as unrewarding and is generally discouraged, except possibly for unusually young patients (especially when precipitated by smoking or use of estrogen-containing hormonal contraceptives) and those in whom revascularization, such as coronary arterial bypass, fails because of rapid occlusion of the graft. Treatment
There is no specific treatment for thrombophilia, unless it is caused by an underlying medical illness (such as nephrotic syndrome), where the treatment of the underlying disease is needed.