Deep vein thrombosis (DVT) is the formation of blood clots (thrombi) in the deep veins. It can lead to complications such as postphlebitic syndrome, pulmonary embolism and death. DVT has genetic and acquired risk factors. The genetic risk factors can be subdivided into those that are strong, moderate and weak. Strong risk factors are deficiencies of antithrombin, protein C and protein S. Moderately strong risk factors are factor V Leiden, prothrombin 20210A, non-O blood group and fibrinogen 10034T. There are many weak genetic risk factors, including fibrinogen, factor XIII and factor XI variants. Acquired risk factors include surgery, oral contraceptives, trauma, obesity, cancer, and so on. In some patients, venous thrombosis occurs in the presence of such risk factors for DVT. These patients are classified as having secondary DVT. In the other patients, no predisposing factors are found, and thus, are considered as having an idiopathic DVT.
