Deep Vein Thrombosis of the Legs: What It Is, Why It Occurs, and Why It Is Dangerous

Deep vein thrombosis is a blood clot in a vein that lies deep in the leg. This blockage is more dangerous than it seems. I explain step by step what happens and at what point you must not delay.

Deep vein thrombosis: what it is

Deep vein thrombosis (DVT) is a condition in which thrombi form in the deep veins, most often in the vessels of the lower limbs. According to various estimates, 10–20% of the population encounters it, and the prevalence ranges from 50 to 160 cases per 100,000 people. Most often the clot forms in the calf or thigh.

If the vein swells with a thrombus, the condition is called thrombophlebitis. It also happens that no obvious cause is found.

Why thrombi form in the veins of the legs

A clot in a deep vein appears when the blood clots more easily than usual, with low mobility and dehydration. The risk is higher if you are over 60 years old, are overweight or obese, smoke, or have already had thrombosis. The list of causes includes hormone replacement therapy, combined contraceptives with estrogen, cancer, heart failure, varicose veins, thrombophilia (the blood clots more easily than usual), inflammatory bowel diseases, and vasculitis.

Certain situations increase the chances temporarily: hospital stay and recent discharge, especially with low mobility; surgery; bed rest for three days or longer; travel longer than four hours by plane, car, or train; pregnancy and six weeks after childbirth; dehydration. Hereditary clotting characteristics also count — antithrombin deficiency, protein C and S deficiency, factor V Leiden mutation.

How thrombosis differs from varicose veins and vein inflammation

Varicose veins are enlarged superficial veins that are visible under the skin. By itself it is not thrombosis, but varicose veins are included in the list of DVT risk factors. Deep vein thrombosis affects veins that lie deep in the leg.

If a vein in the leg has become inflamed, that is a different condition. When a vein with a thrombus swells and becomes inflamed, it is called thrombophlebitis. The exact diagnosis is made by a doctor after an examination, such as ultrasound.

Symptoms: how vein blockage manifests

• throbbing pain in one leg, rarely in both, usually in the calf or thigh;
• swelling of one leg, rarely of both;
• the skin around the painful area is red, bluish, or darkened; on brown and dark skin this is harder to notice;
• swollen veins;
• warmth and tenderness over the vein.

If the thrombus is in a vein of the arm, the same signs will be on the arm. Occasionally the only complaint is lower abdominal pain: this happens with thrombosis of the pelvic veins.

How the diagnosis is confirmed

If DVT is suspected, the person is referred to a hospital for an ultrasound scan within 24 hours. The scan shows whether blood flows through the vein normally. The set of examinations for suspected thrombosis also includes a D-dimer test, Doppler ultrasound of the veins, and venography — a study of blood flow in the veins. What exactly is needed in your case is decided by the doctor.

Complications and when urgent help is needed

The main danger is the detachment of the thrombus. The clot travels with the blood to the lungs and causes pulmonary embolism. This condition is life-threatening and requires immediate treatment. Without treatment, deep vein thrombosis causes 3–15% of deaths from pulmonary embolism. A late complication is post-thrombotic syndrome: after thrombosis the vein works worse.

Deep vein thrombosis by itself is not a reason to call an ambulance; 103/112 — if shortness of breath or chest pain is added to the pain and swelling of the leg.

The text is for reference and does not replace a doctor's consultation: the decision on examination and care is made by the doctor after an examination.

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