The average patient had 173.8 mL of blood drawn for testing, or about half a unit of whole blood. That was about 100 mL higher than the blood drawn in patients who didn't develop moderate-to-severe anemia, according to the researchers.
There were also differences in the amount of blood drawn from hospital to hospital.
"Because we see such a significant variation, chances are that one of the reasons for the variation is hospital-based processes of care," Kosiborod said. "Some hospitals draw more blood than others."
Fortunately, the authors have identified a couple of seemingly simple fixes to this problem.
One option would be to use smaller pediatric tubes to draw the blood rather than adult-sized tubes.
"Pediatric tubes are perfectly adequate for most of the tests that need to be done and can drastically reduce the amount of blood lost," Kosiborod said.
Fewer blood draws also would help, and it may be possible to use blood already drawn and already in the lab for subsequent tests.
But the findings aren't enough to conclude that unnecessary tests are being done, Kosiborod said.
Less testing could also result in medical problems and this study didn't look specifically at how appropriate the tests were.
But there may be an added benefit to doing fewer blood tests.
"We're spending a lot of money on these tests that [can be] unnecessary]," said Dr. Stephanie Rennke, lead author of an accompanying editorial and an assistant clinical professor of medicine at the University of California, San Francisco (UCSF). "If you put the cost together with the issue of the hazard of patients developing hospital-acquired anemia, that's pretty profound."
According to Rennke, UCSF has already tightened up its protocol for ordering blood tests. "We have to think before we order a test," she said.
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