Thrombosis is the formation or presence of a blood clot ("thrombus") in a blood vessel. It can be situated in any vein or artery. If the thrombus breaks loose and travels through the bloodstream, it is called thromboembolism.
Deep vein thrombosis (DVT) occurs when the clot forms in a deep vein. If it travels to the lung, it is called a pulmonary embolism (PE). A thrombus can also lodge in the heart, or calcifications in the neck arteries can break off and travel deep into the brain. Embolism in the brain is called a stroke.
Venous thromboembolism (VTE) is a term that covers deep vein thrombosis (DVT) and/or pulmonary embolism (PE). VTE causes significant morbidity and mortality, and has become a public health concern. Data from the Center for Disease Control and Prevention indicate that between 300,000 and 600,000 people in the US suffer from VTE annually, and approximately 10,000-60,000 die. (To put this into perspective, about 40,000 women die from breast cancer each year.)
Over 100 years ago, Rudolf Virchow, a famous German physician praised as the founder of the social and public health care system in Europe, recognized and described this process. He postulated that three conditions are necessary to form thrombi: venous stasis, vessel injury and hypercoagulability. This became known as the Virchow Triad, and the concept still holds today. Based on it, we have learned to understand hereditary genetic and acquired predispositions to experience VTE. Basic scientific laboratory work, retrospective analyses of patient cohorts, and prospective clinical trials have advanced our understanding of VTE, including its prevention and treatment.
Inherited tendency to thrombi or blood clots is often called thrombophilia. Inherited thrombophilia factors are genetic mutations or absence of factors that play a role in hemostasis, including:
- Factor V Leiden
- Protein C deficiency
- Protein S deficiency
- Antithrombin III deficiency
- Aberrations of the fibrinolytic system
Some of these genetic mutations are very rare and require specialized lab tests and knowledge for diagnosis. The most important determinant of a genetic predisposition is a positive family history. However, in approximately 50% of all patients with a positive family history, the genetic defect cannot be identified by current diagnostic tests.
Conditions that can contribute to thrombosis include:
- Hormonal contraceptives
- Pregnancy and the post-partum period
- Long airplane rides
- Inflammatory bowel disease
- Old age
- Myeloprolifertive disorders
For more facts, statistics, complications, current recommendations and scholarly articles for the public, see the Centers for Disease Control and Prevention's Deep Vein Thombosis / Pulmonary Embolism website.
Also see stop the clot for information suitale for patients and health care professionals.