NEW YORK (AP) – Screening smokers for cancer with lung scans can lead to a high rate of false alarms, unneeded tests and biopsies, a new study suggests.

Some hospitals are promoting lung cancer screening with a special X-ray called a CT scan. And some advocacy groups encourage current or former smokers to get tested.

However, there's no convincing evidence that such tests save lives, and no doctors group recommends routinely screening smokers who don't have symptoms of lung cancer. Government researchers are studying whether the scans could save lives.

While researchers are still waiting for the answer to that, they do have results on just how often scans are wrong. Scientists with the National Institutes of Health say doctors and people considering lung scans should take into account the high risk of false alarms in their study of 3,200 people.

For those who got CT scans, the risk of a "false-positive" – finding a harmless spot – was 21 percent after one scan and 33 percent after two. For chest X-rays, the risk was nine percent after one, and 15 percent after two.

Anything suspicious detected through screening often needs to be followed up with more tests, biopsies and even surgery to find out if it really is cancer. Complications can include lung collapse, bleeding and infection. "You need to know ahead of time" about the risks, said the study's lead author, Dr. Jennifer Croswell, of the NIH's Office of Medical Applications of Research. "Once you have the test, you just can't back out of that."

The study's findings are published in this week's Annals of Internal Medicine.

Lung cancer is the deadliest cancer. Last year, an estimated 159,000 Americans died of the disease. It usually isn't diagnosed before symptoms appear.