Two general forms of hypercoagulability exist: hyperreactivity of the platelet system, which results in arterial thrombosis, and accelerated activity of the clotting system, which results in venous thrombosis. Hypercoagulability refers to an unnatural tendency toward thrombosis. The thrombus is the actual insoluble mass (fibrin or platelets) present in the bloodstream or chambers of the heart.

Conditions and classifications associated with hypercoagulability include the following:

Platelet abnormalities. These conditions are associated with arteriosclerosis, diabetes, increased blood lipids or cholesterol levels, increased platelet levels, and smoking. Arterial thrombosis may be related to blood flow disturbances, vessel wall changes, and increased platelet sensitivity to factors causing platelet adherence and aggregation.

Clotting system abnormalities. These are associated with heart failure, immobility, artificial surfaces (e.g., artificial heart valves), damaged vasculature, use of oral contraceptives or estrogen, pregnancy and the postpartum state, and the postsurgical state. Other influences include malignancy, myeloproliferative (bone marrow) disorders, obesity, lupus disorders, and genetic predisposition.

Venous thrombosis. This can be related to stasis of blood flow, to coagulation alterations, or to increases in procoagulation factors or decreases in anticoagulation factors (Table 2.8).