Often, this anemia persists for a month or more after discharge and could spell worse outcomes -- even death -- down the line, according to a study in the Aug. 8 online edition of the Archives of Internal Medicine.
"This is not just a lab abnormality," said study senior author Dr. Mikhail Kosiborod, a cardiologist with St. Luke's Hospital Mid-America Heart & Vascular Institute in Kansas City, Mo. "These patients actually feel worse after they leave the hospital. Mortality is higher, too."
People with anemia have too-low numbers of the red blood cells that carry critical oxygen to different parts of the body.
The researchers had previously found that about half of heart attack patients who are admitted to the hospital with normal red blood cell, or hemoglobin, counts actually leave with new anemia.
But the majority of these patients had no bleeding complications that could account for the condition.
That led Kosiborod and his colleagues to hypothesize that it was due to the amounts of blood drawn for routine diagnostic tests.
"Drawing blood in a hospital is typically a very common occurrence, particularly in the intensive care unit," said Kosiborod, who is also an associate professor of medicine at the University of Missouri in Kansas City.
The study authors looked at electronic medical records for almost 18,000 patients who'd had a heart attack at one of 57 U.S. hospitals.
While all had normal hemoglobin levels when they were admitted, 20 percent developed moderate-to-severe anemia by the time they left the hospital.
The risk of anemia rose 18 percent for each 50 milliliters (mL) drawn.
"That was probably somewhat more than what we initially expected to find," Kosiborod said.
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.
SOURCES: Mikhail Kosiborod, M.D., cardiologist, St. Luke's Hospital Mid-America Heart & Vascular Institute, and associate professor, medicine, University of Missouri, Kansas City; Stephanie Rennke, M.D., assistant clinical professor, medicine, University of California, San Francisco; Aug. 8, 2011, Archives of Internal Medicine, online
[eng][=green]Diagnosis is an ART