Editor’s note: This is one in a 10-part series of the top medical research advances of 2016 as determined by the American Heart Association.

Like a scene from the movies, a fainting spell can be brought on by sudden emotional distress. Sometimes, severe dehydration or standing still for too long can lead to a blackout.

But when unexplained fainting leads to hospitalization, blood clots in the lungs may be the reason far more often than doctors realize, according to a new study.

Italian researchers found that such potentially deadly lung clots – known as pulmonary embolisms – were found in about 17 percent of the elderly patients they examined. That’s about one out of every six patients.

The study’s findings, published last October in the New England Journal of Medicine, could prompt doctors to start screening patients for something that normally isn’t on their checklist. They also led the American Heart Association to rank the study among its top 10 heart and stroke science advances of 2016.

Researchers in the Pulmonary Embolism in Syncope Italian Trial screened 560 patients admitted to 11 hospitals for first-time episodes of fainting, also known as syncope. The average patient age was 76.

The lead researcher, Paolo Prandoni, M.D., Ph.D., said the findings could have a lifesaving impact by helping to identify a very treatable condition.

“Whenever a patient with a first episode of syncope is admitted to a hospital ward, unless he or she is already on anticoagulation medicine, a pulmonary embolism should be suspected,” he said.

A pulmonary embolism is a clot that breaks free from a vein, usually in the leg, and travels to the lung, where it gets stuck and blocks some or all of the blood supply. Every year, an estimated 300,000 to 600,000 Americans either get pulmonary embolisms, deep vein thrombosis (blood clots in their legs), or both, according to government figures. An estimated 60,000 to 100,000 will die from them.

If doctors believe a lung clot may be behind the fainting spell, the study suggested that additional screenings be conducted, such as a blood test known as a D-dimer that can help rule out a lung clot, and a specific assessment that estimates pretest clinical probability based on various factors.

Those results can determine whether more tests, such as a CT scan, are warranted and, if so, “a therapeutic dose of an anticoagulant drug should be promptly administered while awaiting the imaging tests, according to the available recommendations delivered by all major international guidelines for patients with a high probability of pulmonary embolism,” Prandoni said.

In his study, Prandoni and fellow researchers noted that while checking for blood clots is included in most textbooks for diagnosing fainting spells, current international guidelines “pay little attention” to that possibility.

“Hence, when a patient is admitted to a hospital for an episode of syncope, pulmonary embolism — a potentially fatal disease that can be effectively treated — is rarely considered as a possible cause,” the study’s researchers wrote in their report.

Cardiologist and electrophysiologist Jose Joglar, M.D., agreed.

“That is the reason why this study is unique. It puts the possibility of blood clots as a reason for patients who have to be hospitalized with fainting, and that is something that historically had not been considered as a common cause by physicians,” said Joglar, a professor of internal medicine at UT Southwestern Medical Center who was not involved in the study.

“Before this study, the prevalent belief was that you have fainting because there might be a serious heart rhythm problem, for example. But few had in their minds the possibility that these patients had blood clots in their lungs,” he said.

That is, unless those patients had severe and obvious symptoms.

“For you to faint [from blood clots], the belief was that it had to be so serious and severe that it would present to the hospital with additional signs that would alert the emergency [department] physician of the possibility of blood clots in your lungs,” he said. “But in this study, a large number of those patients were not that sick.”

Joglar hopes the findings from the study will encourage more doctors to automatically consider pulmonary embolism as a possible reason behind patients hospitalized for fainting.

“It will be changing my practice, for sure,” he said, adding that he will be more likely to order D-dimer blood tests and other screenings for candidates considered high-risk.

“The good news in all of this is that should a pulmonary embolism be present, then that’s a treatable condition,” Joglar said. “If treated, it is not a death sentence.”