Deep Vein Thrombosis: What It Is, Causes, and Why It Is Dangerous

Deep vein thrombosis is a blood clot in a vein lying deep within the muscles, most often in the calf or thigh. The diagnosis means not "bad veins" in general, but a specific condition with a specific risk that can be assessed. Below is what is known about the causes, symptoms, and examinations.

What deep vein thrombosis is

The veins of the lower limbs work as a return pipeline: blood flows against gravity, and the valves inside the vessel act as check valves that prevent the flow from turning back. A thrombus in a deep vein blocks the lumen partially or completely — like a plug in a pipe. If the vein also becomes inflamed and swollen, the condition is called thrombophlebitis. Deep vein thrombosis occurs in 10–20% of the population, with prevalence estimated at 50–160 cases per 100,000 population. The veins of the lower limbs are affected more often; in deep vein thrombosis of the upper limbs, the likelihood of a fatal outcome is extremely low.

Causes and risk factors of venous thrombosis

The risk is higher in people over 60 years of age, with excess body weight or obesity, smoking, a previous thrombosis, use of hormone replacement therapy and combined oral contraceptives, including the patch and vaginal ring containing estrogen. The list includes cancer, heart failure, varicose veins, thrombophilias, inflammatory bowel disease, vasculitis, as well as congenital deficiencies of antithrombin, proteins C and S, and certain mutations of the hemostasis system. Situations are also distinguished separately:

• hospitalization and forced immobility, surgery, an implanted device (e.g., a pacemaker);
• bed rest for 3 days or more;
• a trip lasting more than 4 hours by plane, car, or train;
• pregnancy and 6 weeks after childbirth;
• dehydration.

Sometimes thrombosis occurs without an obvious cause — then the doctor looks for a hidden factor.

Forms of thrombosis and possible consequences

The thrombus may be located in various deep veins — for example, in the veins of the calf or thigh. Occlusive forms, in which the lumen is completely closed, and mural forms are distinguished. A long-term consequence of thrombosis is post-thrombotic syndrome, which develops later.

Signs of deep vein thrombosis

The typical picture is throbbing pain in one leg (rarely in both), usually in the calf or thigh; swelling of one leg; redness, bluish discoloration, or darkening of the skin over the painful area, which is harder to notice on brown and black skin; dilated superficial veins. A feeling of warmth and tenderness over the vein are also described. If the thrombus is in the arm, symptoms occur in the arm. Sometimes the only sign is pain in the lower abdomen, but this variant, associated with the pelvic veins, is rare.

How thrombosis is diagnosed

When deep vein thrombosis is suspected, the doctor orders an ultrasound scan of the veins: it shows whether blood flows through the vein normally. Other studies are also used — D-dimer, Doppler ultrasound of the veins, venography. If the cause is unclear, the doctor orders additional tests to find it. The approach is determined by the doctor.

Complications and when urgent help is needed

The main danger is detachment of the thrombus and pulmonary embolism: the clot travels through the venous system and gets stuck in the vessels of the lungs, like a plug in a narrow filter. Without treatment, deep vein thrombosis causes 3–15% of deaths from pulmonary embolism, and pulmonary embolism itself requires immediate help. A late complication is post-thrombotic syndrome.

Pain and swelling of the leg are not in themselves a reason to call an ambulance. You should call 103 or 112 if shortness of breath or chest pain appears against the background of pain and swelling — these are signs of pulmonary embolism.

This material is for reference: it describes the condition and its signs, but does not replace consultation with a doctor, who assesses the specific situation.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer