The term thrombophilia refers to the condition of patients who have a particular susceptibility to thrombosis.

Thrombophilia can be "primitive" or "constitutional" (presence of a genetic abnormality) or "secondary" or "acquired" (due to an acquired disease that disrupts coagulation).

The blood is maintained in a liquid state only by the existence of a coagulation inhibitor beside the coagulation activators. The quantitative or qualitative imbalance of these factors will lead to thrombophilia.

The genetic origin of constitutional thrombophilia can be demonstrated in about one in two patients with deep vein thrombosis.

The abnormalities are due to deficits in physiological inhibitors of coagulation or, conversely and much more rarely, to hypofibrinolysis. This may be related to an excess of tissue plasminogen activator inhibitor and urokinase (PAI-1), or a lack of tissue plasminogen activator (tPA).

The factor V Leiden mutation causes thrombophilia, an increased tendency to form abnormal blood clots in the blood vessels. This mutation has been observed in patients with idiopathic thrombotic manifestation.