WASHINGTON (AP) -- If you're lying in a hospital bed, chances are doctors didn't check you for a silent killer -- one that causes some 60,000 potentially preventable deaths a year.

It's called "deep vein thrombosis," when a dangerous blood clot forms deep in the leg muscles. The clot sometimes floats into the lungs, causing sudden death.

Such clots made headlines a few years ago when seemingly healthy people collapsed after long airplane flights. Take an overseas flight today and you'll probably see a video advising walking around or at least wiggling your legs frequently to keep clots at bay.

While that's good advice, it provides a skewed vision of the clots: Most actually occur when people are hospitalized for surgery, trauma or some other reason. Worse, although simple steps can prevent blood clots in hospitalized patients, troubling new research suggests too many physicians either don't know to check for the risk or they forget.

Now a group of doctors and federal health officials are trying to raise public awareness of DVT, so more physicians will check for it -- and so people at risk can take steps to protect themselves, whether they're entering the hospital or taking a long trip.

"There are so many preventable deaths," laments Dr. Samuel Goldhaber of Harvard Medical School. "It's become a crisis."

Goldhaber is conducting the largest study ever done on who gets DVT and why, using a registry of 5,000 DVT patients from 180 hospitals. Findings so far are "quite shocking," he said: More than half of people who developed DVT while hospitalized for other reasons never got the clot-preventing care that doctors should have administered.

There aren't precise counts, but officials estimate up to 2 million Americans suffer DVT each year. In as many as 600,000, the clot moves to the lungs, called a pulmonary embolism. Anywhere from 60,000 to 100,000 of them die. Survivors often must take the blood-thinning drug warfarin for years to prevent recurrence.

Veins have a hard job fighting gravity as they push blood from the legs back up toward the heart. Illness, injury or prolonged inactivity can inhibit that action, allowing blood to temporarily pool where clots can form.

Risk factors include:

-Hospitalization for a serious illness or surgery.

-Other immobility, such as paralysis or long-distance travel, by plane, train or car.

-Obesity.

-Excess estrogen during pregnancy or from birth control pills or hormone therapy.

-Smoking.

-An inherited tendency for sticky, clot-prone blood.

-Being over age 40.

-Chronic diseases such as high blood pressure, heart disease or cancer.

But it can strike anybody, warns Miranda Fowler of Clarendon, N.C., who got a DVT at age 22 while competing in the Miss North Carolina pageant. It felt like an excruciating leg cramp, leaving her unable to stand after a long car trip. Paramedics dismissed her complaint; fortunately, a friend called a doctor who sent her to the emergency room.

Fowler unknowingly had three DVT risks: Her grandmother had developed blood clots, and she'd inherited the tendency. Her doctor didn't ask about that family history before prescribing birth control pills. The final straw was sitting motionless in a car for hours.

But patients don't always experience leg pain to know they have a DVT. And if the clot heads for the lungs -- symptoms then range from a general sense of anxiety to shortness of breath or passing out -- it can be too late. For 20 percent of patients, sudden death is the first symptom, says Dr. John Heit of the Mayo Clinic.

Hence the new focus on preventing clots.

The Centers for Disease Control and Prevention and the American Public Health Association brought DVT experts together last week to debate how. They called for hospitals to screen all patients for DVT risk factors and do better preventive care -- injections of a blood-thinning drug called "low molecular weight heparin" that cuts clots by two-thirds, and compression stockings to help leg veins pump for those who can't take the drug.

People can protect themselves, too. Goldhaber's advice:

-Learn the risk factors, and know if you have a family history of blood clots.

-Ask a doctor about preventive care before any surgery or hospitalization, or during pregnancy.

-Move around when traveling. If you're at high risk, ask a doctor about wearing compression stockings or getting a blood-thinning injection for super-long travel.

-Seek immediate care if you have any symptoms of a clot.

Copyright 2003 The Associated Press. All rights reserved.