This Oct. 13 marks the first-ever World Thrombosis Day, a day of awareness about thrombosis — a blood clot that forms in an artery or vein. Thrombosis can cause the world’s top three cardiovascular killers: heart attack, stroke and venous thromboembolism, or VTE.

Many people know about heart attacks and strokes, but not everyone has heard about VTE. Let’s break it down. When a blood clot forms in one of the deep veins — usually in the lower limbs, such as the thigh or calf — leading to either partially or completely blocked circulation, this is called a “deep vein thrombosis,” or DVT. Symptoms may include pain, tenderness, swelling or discoloration of the affected area and skin that is warm to the touch, though only about half of people with DVT experience symptoms. DVT affects approximately two million Americans every year.

When a fragment of the DVT breaks off and travels from the leg up to the lungs, where it blocks a pulmonary artery or one of its branches, it is called a pulmonary embolism, or PE. Patients with PE may experience shortness of breath, an apprehensive feeling, chest pain, rapid pulse, sweating or a bloody cough.

Together, the conditions of DVT and PE are referred to as venous thromboembolism, the No. 3 cardiovascular killer worldwide. Half a million people die from VTE each year. In the U.S. and in the U.K., that’s more than the combined death total from AIDS, highway accidents, and breast and prostate cancers.

A blood clot in the leg and lungs can happen to anyone at any age. Some people do not have any warning signs or symptoms, so it’s important to know the risk factors. The main triggers for the formation of blood clots are:

— Prolonged immobility from hospitalization, bed rest or long-distance travel. In fact, being in the hospital for an extended time leads to more than two-thirds of all cases of blood clots in the leg.

— Patients with damage to their vein walls because of injury or surgery, especially hip and knee surgery.

— Those with blood-clotting issues because of an acquired state, like cancer or pregnancy, or because of a genetic disorder.

This is, by no means, a complete list. Pregnant women, seniors and those with a family history of blood clots also are at risk. It’s important to remember risk factors can be compounded. For example, combining recent hip surgery with a long airplane flight can raise the risk of developing thrombosis. However, having multiple risk factors doesn’t mean you will get a blood clot.

VTE is a potentially life-threatening emergency in need of immediate medical attention. To learn about the risk factors, signs and symptoms, and prevention of thromboses, visit

Death from VTE is preventable, especially if you talk to your doctor and educate yourself.

Dr. Cindy Asbjornsen, founder of the Vein Healthcare Center in South Portland, is certified by the American Board of Venous and Lymphatic Medicine.