Thrombophlebitis is a condition in which a blood clot (a thrombus) has formed inside a vein, causing the surrounding veins to become inflamed (phlebitis). There are two types of thrombophlebitis: superficial vein thrombosis (SVT) and deep vein thrombosis (DVT). SVT imposes less medical risk, although it may be a warning sign of the more serious DVT, especially if it occurs in the long veins of the extremities. However, DVT can be life–threatening if the blood clot or pieces of the blood clot break loose and travel to another part of the body, lodging in another blood vessel and causing an embolism. If pieces of the clot lodge in an artery of the lungs, it could cause a potentially fatal pulmonary embolism.

A number of factors can contribute to the formation of blood clots. These factors include disease, injury or surgery. People at higher risk for forming blood clots include those who smoke, are obese or who are pregnant. Symptoms of thrombophlebitis include swelling, tenderness and throbbing. Anticoagulant medications are generally the first line of treatment for the condition. If the potential danger persists despite treatment (e.g., the clot will not dissolve), then more invasive procedures may be necessary.