Many kids get plasma transfusions when there's little evidence they do much good, according to a new study.

Transfusions of so-called fresh frozen plasma are sometimes given to both kids and adults whose blood has problems clotting, or if they have lost a lot of blood from surgery or an accident.

But only a couple of studies in kids have shown that plasma transfusions are a good option for one specific heart surgery procedure. The rest of the time, researchers have found they don't work, or that their benefit is uncertain.

In the current study, pediatricians reported that almost three percent of kids admitted to children's hospitals in the U.S. had a transfusion. More than half of the transfusion recipients were under a year old, a third had heart disease and 70 percent were critically ill.

"For all we know, it may be used entirely appropriately," said Dr. John Puetz, from Saint Louis University, who worked on the study.

"The problem is, we don't have the evidence base... to demonstrate what's inappropriate use and what's not inappropriate use."

"The concern," he told Reuters Health, "is a fair number of children are being exposed to (fresh frozen plasma) without published data showing what it's effective for."

The problem with that, researchers said, is that the transfusions always come with a risk of side effects and complications, which range from allergic reactions to heart failure, if doctors give kids more plasma than their hearts can handle.

Puetz's team consulted a database of about 3.2 million admissions to 40 different children's hospitals in the last decade. According to hospital records, just under three percent of those kids got a plasma transfusion, most in the intensive care unit.

The researchers couldn't tell why the plasma was used in each case, or how much of it kids got. But only about one-third of the kids' records also showed they had a heart procedure known as a cardiopulmonary bypass -- when a pump does the job of the heart and lungs during surgery, and a plasma transfusion (along with red blood cells) is indicated.

There were 24 recorded cases of acute lung injuries related to the transfusions, but the authors write in the Journal of Pediatrics that it's hard to tell how many kids had other complications.

"The biggest reason not to give any transfusion... is the risk of the complications that you can have," said Dr. Lorne Holland, of the Nashville-based pathology services company PathGroup, Inc., who has researched the use of fresh frozen plasma. That would include lung injuries and congestive heart failure, as well as more minor itchy allergic reactions.

Still, Puetz added, "No one's really looked to see what all the possible side effects may be."

A typical plasma transfusion would cost a few hundred dollars, Holland said.

He thinks that too many kids are still getting the transfusions, despite the general lack of evidence that they work -- or are better than other alternatives such as whole-blood transfusions in certain cases.

"I think the numbers in that study and ones in adults are too high," Holland, who was not involved in the study, told Reuters Health. "A lot of physicians are convinced by evidence of, 'That one patient, that one time, seemed to do better when I gave it to them.'"

Puetz said it's still not clear whether plasma transfusions are being done too often, based on the lack of data. He called for more critical studies to see if fresh frozen plasma transfusions really do work in all of the cases where they're commonly used in kids.