KANSAS CITY, Mo. — A stay at the hospital can be draining in more ways than patients and doctors realize, researchers at St. Luke’s Hospital of Kansas City say.

Those frequent tests that suck tube after tube of blood out of patients’ arms can lead to anemia serious enough not only to leave patients tired and short of breath but to even raise their risk of dying.

“A lot of the blood work done in a hospital is very important and necessary,” said St. Luke’s heart specialist Mikhail Kosiborod. “But the volume of blood drawn is a risk factor. This hasn’t been on the radar screen. We don’t think about there being a downside (to blood tests).”

Doctors have long assumed that hospital-acquired anemia was caused by bleeding during surgery, Kosiborod said. But anemic patients are no more likely to suffer such complications, he said.

Kosiborod said he and the team of researchers from St. Luke’s and several other medical centers are the first to trace the likelihood of acquired anemia among heart attack patients to the number of blood tests they receive.

In a study published online Monday by the journal Archives of Internal Medicine, the researchers looked at data on more than 17,000 heart attack patients from 57 hospitals nationwide.

none of these patients had anemia — depleted levels of red blood cells that carry oxygen — when they entered the hospital, but one in five developed moderate to severe anemia during their hospital stay. The more blood they had drawn, the greater was their risk.

On average, the patients with hospital-acquired anemia had a total of 6 ounces of blood drawn, twice as much as the patients who didn’t become anemic. At some hospitals, total blood draws averaged as much as 8 ounces among anemic patients.

That may not seem like much; it’s roughly half or less than what a blood donor gives at one sitting.

But blood donors are healthy volunteers, Kosiborod said. Their bone marrow can replenish red blood cells quickly.

“People who are healthy, they won’t even feel (the blood loss),” he said. “Hospital patients are not healthy people. Their bone marrow isn’t as capable.”

Previous research by Kosiborod and his St. Luke’s colleagues found that months after leaving the hospital, heart attack patients with acquired anemia were having a harder time than non-anemic patients doing everyday activities such as housework and shopping.

Fatigue from the anemia may make heart attack survivors reluctant to go back to work or do the supervised exercise that is key to cardiac rehabilitation, said Adam Salisbury, also a St. Luke’s heart specialist and lead author with Kosiborod on the new study.

“We think that can be a significant barrier to the lifestyle changes they need to make,” Salisbury said.

Even more concerning, the St. Luke’s researchers have found that patients were 82 percent more likely to die within a year of their heart attack if they had developed moderate to severe anemia while they were in the hospital.

Although the St. Luke’s researchers haven’t studied patients who have been hospitalized for reasons other than heart attacks, they think that other patients, particularly those in intensive care units where daily blood draws are common, are also at risk of developing anemia.

“These patients may have more trouble recovering,” Salisbury said.

Tracing hospital-acquired anemia to blood tests opens several possible solutions to the problem that St. Luke’s already has starting working on:

Technology has improved to the point where less blood is needed for many tests. In most cases, traditional blood collection tubes that hold about 0.14 of an ounce can be replaced with tubes that hold about half as much.

Hospital laboratories often keep blood samples for several days. When doctors order a different type of test for patients, the labs can use the blood they have on hand, rather than a new sample.

Instead of ordering routine tests on set schedules, doctors may consider spacing tests at longer intervals as patients improve and their conditions stabilize.

“It’s important how much blood we drain from patients and it’s important to minimize it,” Kosiborod said.