Thrombosis

Thrombosis means a blood clot (a thrombus) has formed inside a vein or artery. Clotting is normal when you are cut, but a clot that forms inside a vessel can partly or fully block blood flow. Doctors separate venous thrombosis, in the veins, from arterial thrombosis, in the arteries, because the causes and dangers differ.

The most common venous form is deep vein thrombosis (DVT), usually in the leg. The National Heart, Lung, and Blood Institute groups DVT and pulmonary embolism together as venous thromboembolism (VTE), because a clot in a deep vein can break loose and lodge in the lungs. Arterial clots are the kind that cause most heart attacks and strokes.

Risk factors include surgery, long periods without moving, cancer, pregnancy, estrogen-containing medicines, and devices placed inside blood vessels. Signs of DVT can include swelling, pain, warmth, or redness in one leg. Sudden shortness of breath or chest pain can mean a clot has reached the lungs and needs emergency care.

Thrombosis shows up often in product liability cases. Implanted devices that sit in the bloodstream, like port catheters, have been the subject of lawsuits alleging they led to clots, and drug cases sometimes turn on whether a label adequately warned about clotting risk. Proving a claim usually means showing the diagnosis in medical records and linking it in time to the product. See the Bard port catheter lawsuit page, and our explainer on class actions versus mass torts, since injury cases like these are usually filed individually rather than as a class.