Deep Vein Thrombosis (DVT) is the formation of a blood clot in a vein deep within the body, usually in the legs. This condition is related to a more severe condition called pulmonary embolism (PE), which occurs if the clot breaks free and travels through the circulatory system to the lungs. DVT always precedes PE. It is estimated that about 250,000 people are hospitalized with venous DVT in the United States each year, but the incidence is probably much higher as many cases go undiagnosed. Pulmonary embolism is potentially life-threatening if prompt medical attention is not received. Therefore, recognizing the symptoms of venous DVT and avoiding risk factors is of paramount importance. Activated protein C is a protein with potent anticoagulant properties. During the normal blood clotting process, Activated protein C limits clot formation. 5% of healthy individuals have resistance to Activated protein C, which is associated with a sevenfold increase in the risk for deep vein thrombosis. Activated protein C resistance is associated with heterozygosity or homozygosity for a single point mutation in the factor V gene (Factor V Leiden) People who are homozygous for F5 rs6025 are likely to have a higher-than-average risk of developing blood clots. This effect was more predominant in women, likely due to the effect of oral contraceptives. Because of the increased risk of thrombosis with age, the absolute risk becomes most pronounced in older patients, both for heterozygous and homozygous individuals. People with the F5 CC genotype may still be at risk for DVT due to coexisting genetic thrombophilic disorders, which have a supra-additive effect on overall thrombotic risk; Acquired thrombophilic disorders: antiphospholipid antibodies, hyperhomocysteinemia, high factor VIII levels, malignancy and circumstantial risk factors such as long-distance travel, central venous catheters, pregnancy, oral contraceptive use, hormone replacement therapy (HRT), selective estrogen receptor modulators (SERMs), organ transplantation, advancing age, and surgery. The absolute risk for DVT becomes most pronounced in older patients because of the increased risk of thrombosis with age, both for heterozygous and homozygous individuals. For the homozygous individuals, the absolute risk may become several percentage points per year. This implies that most individuals homozygous for factor V Leiden will experience at least one thrombotic event in their lifetime.