Blood that sits can clot, and clots propagate and inflame the vein, causing thrombophlebitis. While painful and uncomfortable, thrombophlebitis is only part of the problem. What is more serious is that small clots could dislodge and pass up through you thigh, into your groin, through your abdomen, and into your heart. Very small pulmonary emboli can probably go unrecognized for a brief time. The large ones can kill almost instantly, and the smaller ones cause a spectrum of damage to the lungs in the form of pulmonary infarctions.
Pulmonary emboli are to be avoided at all costs, so thrombophlebitis needs to be avoided.
Once there are clots in the deep veins, they need to be diagnosed and treated quickly before emboli happen. There are clinical signs and symptoms that suggest thrombophlebitis. For diagnosis, though, your doctor will want to take an actual look at the veins to see if there are any clots. If you were unfortunate enough to have developed thrombophlebitis 10 to 15 years ago, you would have been subjected to a contrast venogram . The first step in a contrast venogram is to insert an IV into the foot, where the veins may not be very good at all.