People who receive blood transfusions may have a high risk of infection depending on how many red blood cells they receive, according to a recent study.

Researchers from the University of Rochester and the University of Michigan found that when the number of blood transfusions is reduced, infection rates fall by 20 percent. Blood transfusions are among the most common treatments for hospitalized patients nationwide.

Transfusions are often used for anemia or during surgery to make up for blood loss.

"The fewer the red blood cell transfusions, the less likely hospitalized patients were to develop infections,"  lead author Jeffrey M. Rohde, M.D., assistant professor of internal medicine in the division of general medicine at the University of Michigan Medical School, said in a statement. "This is most likely due to the patient's immune system reacting to donor blood (known as transfusion-associated immunomodulation or TRIM). Transfusions may benefit patients with severe anemia or blood loss; however, for patients with higher red blood cell levels, the risks may outweigh the benefits."

For the study, which was published in JAMA, researchers analyzed data from 21 randomized clinical studies involving more than 8,700 patients. They found that for every 38 hospitalized patients considered for a red blood cell transfusion, one patient would be spared a serious infection if fewer transfusions were used.

 "Many people are beginning to accept that we can make a difference - despite being taught in medical school that blood transfusions 'might help and can't hurt,'" Neil Blumberg, researcher and professor at the University of Rochester School of Medicine and dentistry, said in a statement. "What we've found is actually the opposite, that it can hurt and it rarely helps."

Approximately 14 million hospitalized patients a year receive transfusions, the study noted. And infections cost hospitals in the United States an estimated $28 to $45 billion annually, according to the Centers for Disease Control and Prevention.

Each infection typically requires an extra $50,000 to treat, and many patients who get infections are already seriously ill, Blumberg said.