Physicians have identified a number of risk factors for deep vein thrombosis (DVT). As many as 80 percent of patients have one or more risk factors, and the risk factors tend to cluster in older people, which may help explain why DVT is more common among people over the age of 50. These risk factors include:
Inherited blood conditions (inherited thrombophilia). There are a number of genetic defects that are associated with an increased risk of venous blood clots. These account for many of the cases of DVT that occur in people under the age of 50. In general, these inherited conditions affect the ability of the blood to clot.
Venous malformations present at birth (congenital venous malformations). Infants born with an abnormal or absent inferior vena cava, which drains blood from the lower extremities, are at increased risk of recurrent episodes of DVT. Also, abnormalities of other veins, including the iliac, which runs inside the thigh, are associated with increased risk of DVT.
Cancer. Patients with cancer are sometimes “hypercoagulable,” meaning their blood clots more easily than others because of blood substances produced as a result of their disease. About 20 percent of patients with symptomatic DVT also have a malignancy, with lung cancer as the most common.
Surgery. The risk of DVT is increased greatly during surgeries including orthopedic, vascular and neurosurgery. The risk level raises when the patient is over age 40, has experienced previous blood clots, has cancer or heart disease, and is confined to a hospital bed for a long period of time. These individuals remain at risk for several days after hospital discharge. Preventive therapy is often recommended to prevent blood clots from traveling to the lungs and causing a possibly fatal pulmonary embolism.
Trauma. All forms of major injury are associated with an increased risk of blood clots and DVT. The reasons are not completely understood, but it may be connected to decreased blood flow to the extremities, immobilization and the depletion of natural anticoagulants, which prevent the blood from clotting, as a result of injury.
Pregnancy. The risk of DVT is raised during pregnancy, possibly as a result of the enlarged uterus obstructing venous blood flow from the legs and hips.
Birth control pills. The use of birth control pills is the leading cause of DVT among young women. Research has shown that the risk of DVT increases within four months of beginning birth control pills and decreases to previous levels within three months of stopping birth control pills.
Hormone replacement therapy. The use of hormone replacement therapy to treat the symptoms of menopause is associated with an increased risk of venous blood clots, including DVT. Hormone replacement therapy usually consists of an estrogen and synthetic progesterone combination.
Immobilization. Prolonged bed-rest or other forms of immobilization are associated with increased risk of DVT.
Travel. At one time, DVT was nicknamed the “economy class syndrome” because of the perception that frequent travel was a risk for DVT. Recent studies, however, have complicated the idea that airline travel alone can raise the risk for DVT. Instead, researchers speculate that the forced immobility of sitting in airline seats is a leading risk factor. Other studies, however, have linked the increase in DVT among airline travelers to dehydration, pressure changes within the airplane as it rises and descends, and the presence of other risk factors.
Heart failure. A condition characterized by the heart’s inability to pump enough blood to meet the oxygen needs of the body. In particular, left ventricle malfunction and atrial fibrillation are associated with DVT.
Seasonal change. Hospitalizations for DVT tend to increase during cold winter months, possibly because of reduced activity during the cold season or vasoconstriction as a result of cold.
Cardiovascular risk factors. There is an overlap between some risk factors for heart disease and risk factors for DVT, including elevated homocysteine obesity and diabetes.
Central venous catheters. The use of central venous catheters is associated with increased risk for DVT, especially among younger patients. These catheters are long, thin tubes that are placed into veins during surgery to administer medications and withdraw fluids.
Previous episodes of venous blood clots. The presence of previous blood clots in the veins is a major risk factor for DVT. Similarly, patients who have experienced pulmonary embolism because of DVT are much more likely to have recurrent episodes of pulmonary embolism.
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