Deep Vein Thrombosis

A deep vein thrombosis is a blood clot that forms in one of the large veins running deep inside the calf, thigh or pelvis. The clot blocks the vein, so blood backs up behind it and the leg swells, aches and feels tight and warm. It is usually one leg, and the swelling comes on over hours or days.

Clots form when blood sits still, when the vein wall is injured, or when the blood itself is stickier than usual. Long flights and long stretches in bed, recent surgery on a hip or knee, a plaster cast, pregnancy and the weeks after delivery, the contraceptive pill, cancer and an inherited clotting tendency all raise the risk, and often two of them stack up.

What decides the treatment is how far up the clot goes and how long it has been there. A clot confined to the calf is treated with blood thinners alone. A fresh clot filling the thigh and pelvic veins in a young person with a badly swollen leg is where your surgeon will consider removing or dissolving it, to protect the valves that clot will otherwise scar.

The examination compares the two legs. Your doctor measures the calf circumference on both sides, looks for swelling that pits under a finger, warmth, and tenderness along the line of the deep veins, and checks whether the veins just under the skin are standing out more on the swollen side.

The test that confirms it is a duplex doppler ultrasound of the leg, which shows whether the vein squashes flat under the probe. A vein full of clot will not. It also shows how high the clot reaches, and that is what changes the plan. A D-dimer blood test is often done first, and a normal result in someone at low risk makes a clot unlikely enough to look elsewhere.

If you are breathless or your chest hurts, a CT scan of the lung arteries is done at the same time, because the two are one illness. Once the clot is confirmed, expect blood tests for kidney function and clotting, and questions about family history, recent travel, surgery and cancer screening.

Blood thinners start on the day of diagnosis and continue for three to six months, sometimes longer if the clot came without a cause or has happened before. The pain and tightness ease over one to two weeks. Walking is encouraged from the first day, since it helps the swelling more than resting does.

Most people are back at desk work within a week. A graduated compression stocking worn during the day for up to two years reduces the aching and swelling that can persist afterwards. If the clot was dissolved through a catheter you spend one to three nights in hospital while the drug runs and the scans are repeated.

What decides whether the leg stays comfortable is how much clot clears and whether the valves survive. A vein that reopens early behaves close to normal. One left scarred and blocked leaves a leg that swells and aches on standing for years, and your doctor will keep you in a stocking to manage it.