Acting Surgeon General Steven Galson issued a "call to action" this week to make more Americans aware of deep-vein thrombosis, life-threatening blood clots that occur in the legs or pelvis. The condition affects 350,000 to 600,000 Americans every year. DVT and pulmonary embolism (lung blood clots; some originate in the legs) kill an estimated 100,000 people annually, according to Galson.

We asked Steven Elias, director of the Center for Vein Disease at Mount Sinai Medical Center in New York, for a primer. Elias says he has no affiliation with drug or medical device manufacturers.

(This is an edited transcript.)

Why is Acting Surgeon General Galson's "call to action" coming now?

We're all thrilled that he's recognizing the problem. In the last couple of years, the public's awareness of vein disease has increased. We had [NBC newsman] David Bloom die of DVT [while embedded with troops in Iraq in 2003]. We have been developing nice, new minimally invasive procedures to treat vein disease. We are looking at diseases that are preventable, and DVT is preventable.

Who's susceptible to DVT?

There are a number of risk factors.

The things that cause clotting are slow flow of blood, damage to the inside of veins from trauma, like if you were hit in the mid-thigh area hard enough to irritate the inside of the veins, and hypercoaguable states that can lead to increased risk of clotting. Usually you need two out of the three to cause the DVT. If everything else is normal, the chance of DVT is quite low.

The most common risk factor is immobility: if you had recent surgery or an accident with, say, a leg fracture and you're not walking around as much.

What are hypercoaguable states?

Hypercoaguable states can be inherited problems that cause clotting. Acquired hypercoaguable states can occur in people with cancer, women on birth-control pills or hormone-replacement therapy, and surgery itself stimulates chemicals that cause a higher chance of clotting.

People will say, "How do I know if I have an inherited disorder?" Someone may have had a mother or father who had a blood clot for no apparent reason — that's one thing. Someone with one or two unexplained miscarriages may also tip you off to an inherited disorder, or someone who has brothers or sisters with clotting problems. Early 50s is the average age of heart disease, so an early heart attack or stroke will be a tipoff to an inherited disorder, like if someone said, "My father had a heart attack at 39."

What are the symptoms of DVT?

Sudden onset of calf pain and leg swelling. The pain is worse when the leg is hanging down. There's warmth to the area because the veins are inflamed.

How is DVT diagnosed?

By having a high index of suspicion and taking a good family or medical history. Have they had a clot in the past or a procedure that would put them at risk, such as total hip or knee replacement?

The diagnosis is made by ultrasound to look at the flow of blood. Ultrasound tells us in 15 or 20 minutes and it's almost 100 percent as to whether someone has it or doesn’t have it.

How is DVT treated?

Traditional treatment has been blood thinners: heparin or coumadin. Blood thinners prevent more clots from developing and give the body time to break up the existing clots on its own.

Treatment nowadays is really minimally invasive. Most use medicines that dissolve the clot and include a mechanical way of breaking up the clot and sucking it out of the body so it can never travel to the heart or lungs. When you put these techniques together, you can dissolve these clots within 24 to 48 hours.

What's the risk of death from DVT?

What kills somebody with DVT is when clots travel from the legs and block the main vessels to heart and lungs. Leg clots travel 2 to 5 percent of the time, though the patient may not die.

How can DVT be prevented?

Prevention is the real key. If we prevent DVT, we don’t have to worry about risks and complications.

Being aware of who's at risk is very important. Guidelines from the American College of Chest Physicians recommend that every patient that enters the hospital be assessed for their risk of developing DVT.

People on flights over 6 hours have a much higher chance of developing DVT — three to four  times the risk of developing a clot. If you're on a long-haul flight, get up once an hour, drink and move around. Even if you're sitting at a desk and you flex your ankles or wiggle your toes, that's sufficient, too.

The general public, if they're not going on long car or plane trips, they don’t have to worry about preventing DVT. A normal, active individual without a family history, if they have no risk factors, don’t worry — worry about something else.