Deep vein thrombosis (DVT)

Deep vein thrombosis is a blood clot forming in one of the deep veins, most often in the calf or thigh. The clot blocks blood returning from the leg, causing swelling, pain and warmth. The serious risk is pulmonary embolism: if part of the clot dislodges, it travels through the heart to the lungs, which can be life-threatening. DVT and pulmonary embolism together are called venous thromboembolism. Clots form when blood flow is sluggish, the blood is more prone to clotting, or a vein is injured — so risk rises with immobility (long flights, hospital stays, surgery), pregnancy and the weeks after birth, cancer, the combined contraceptive pill or hormone therapy, obesity, increasing age, and inherited or acquired clotting tendencies (thrombophilia). It is diagnosed with an ultrasound of the leg, often after a D-dimer blood test, and treated with anticoagulants.

• D-dimer — a breakdown product of clot; a normal D-dimer helps rule DVT out in lower-risk people, but a raised one is non-specific.
• Compression ultrasound of the leg — the main diagnostic test.
• Full blood count, kidney and liver function — baseline before anticoagulation.
• INR / APTT — used to monitor or before starting certain anticoagulants.
• Thrombophilia and cancer screening — considered in unprovoked or recurrent clots.
• Clinical probability score (e.g. Wells) — guides whether to test and how.

• Swelling of one leg (or arm), often the calf
• Pain or tenderness, which may feel like cramp, often when standing or walking
• Warmth and redness or discolouration of the skin over the area
• The leg feeling heavy or tight
• Sometimes no symptoms at all
• Warning signs of pulmonary embolism — sudden breathlessness, chest pain worse on breathing in, coughing (including blood), a fast heartbeat — are a medical emergency