The risk factors involved in the development of deep vein thrombosis (DVT) are strongly linked with its causes.
Risks that may increase a person’s chance of experiencing DVT include:
- Age: Although deep vein thrombosis can happen to anyone, at any time, of any age, risk does typically increase between the ages of 40 to 60 (and older).
- Previous DVT occurrence: Risk increases considerably if deep vein thrombosis has occurred before.
- An inherited blood-clotting disorder: Blood may clot more easily due to a disorder and various other combination of risk factors (depending on the type of disorder). Disorders may include factor V Leiden (a mutation of the blood's factor V protein).
- Sedentary state / prolonged immobility: Those at greater risk include individuals with paralysis, or who have been immobile for a long period due to injurious damage to the veins, following surgery (especially if a catheter is placed in a vein, following major surgery to the abdomen or having a joint replacement procedure – hip, pelvis or knee) or other illness. When the legs are still for a long period, calf muscles do not contract normally, effectively slowing down blood circulation and increasing the risk of blood clots as blood begins to accumulate or pool in the legs.
- Weight: Pregnancy and obesity (being excessively overweight) can increase pressure on the pelvic and leg veins, due to a growing baby or excess body fat. A pregnant woman also experiences increases in hormone levels (especially oestrogen), and slower blood flow as her uterus expands. This can result in blood flow restrictions with less blood able to return to the heart from the extremities. This then elevates risk of DVT during pregnancy and also for at least 6 weeks following the delivery of the baby (as hormone levels return to normal). A pregnant woman may be warned of an increased risk of DVT if bed rest is required, or following a caesarean delivery (C-section).
- Medications: Oral contraceptive pills or hormone replacement therapy (containing oestrogen).
- Medical conditions: Some types of cancer or treatment procedures can result in an increase of substances in the bloodstream. This can stimulate abnormal clotting. Conditions with limited heart (such as heart failure) or lung function (lung disease) may cause clotting and result in organ failure if untreated. Other conditions include Crohn’s disease, ulcerative colitis and other inflammatory bowel diseases. Varicosities may also predispose a person to a higher risk of varicose veins and DVT or thrombophlebitis.
- Smoking habits (heavy usage): Affects circulation and thus increases the risk of blood thickening and the development of clots. Chronic smoking causes a reduction in oxygen levels in the blood. This results in a compensatory mechanism whereby the body produces more red blood cells. This causes blood thickening and “stickiness.”
- Genetics: A family history of DVT or pulmonary embolism may increase risk in future generations.