Washington ? Millions of Americans at risk for a breath-robbing disease leave the doctor’s office every year not knowing they missed out on a simple test that could tell if their lungs have begun scarring and dying.

Just breathing into a little machine can diagnose the nation’s No. 4 killer, called chronic obstructive pulmonary disease, or COPD, a term that encompasses the lung destruction of emphysema and chronic bronchitis.

Half of the 24 million people thought to have COPD don’t know it. Few patients are diagnosed until they’ve lost more than half their lung function and are left breathless merely crossing a room. And deaths are rising, more than 119,000 a year.

Now there’s a move to have patients treated sooner, by getting lung-testing machines once used only by specialists into family doctors’ offices — and having those primary-care physicians test every at-risk person who comes in the door.

Who’s at risk? Smokers and ex-smokers in their 40s, and anyone with shortness of breath, a prolonged cough or increased phlegm.

The bottom line: “The test is easy, and you should do it,” Dr. Barry Make of Denver’s National Jewish Medical and Research Center said as he taught use of the machine, called a spirometer, at a medical meeting last week.

Simply take a deep breath and then exhale as hard and long as you can into the mouthpiece, like blowing out lots of birthday candles. The machine automatically analyzes whether your lung capacity is normal for your age and size. Insurance covers the $30 test.

“This is a disease … that has a very, very negative image,” laments Dr. Sonia Buist of Oregon Health & Science University. “Pitifully little is understood about it in the public.

“The tools we have available can make life better,” she adds. “They’re simply not being used.”

Diagnosis is only the first hurdle. Many patients don’t get the right treatment, either. While there’s no cure, there are ways to help patients preserve their remaining lung capacity.

So the American Thoracic Society is pushing to increase spirometer access, and writing guidelines that will call for anyone at risk to be tested.