Researchers said this advice, if widely adopted, could save thousands of people in the United States each year. Taking care of anemia is probably as important as giving aspirin, beta blockers or clot-dissolving drugs, which are already standard care for heart attacks.
The size of the benefit depends on how anemic people are. But even those with mild cases lower their risk of death by one-quarter during the first month of recovery if they get transfusions. The risk falls by two-thirds among the severely anemic.
Anemia is common among the elderly, and doctors routinely check for it. But there is no consensus about how to use the information, and willingness to give transfusions after heart attacks varies widely among doctors.
"There is very little evidence about the role of anemia in patients having heart attacks or when you should give them blood transfusions," said Dr. Harlan Krumholz of Yale University.
His study confirmed the link between anemia treatment and survival in a review of 78,974 Medicare patients treated for heart attacks in 1994 and 1995. The results were published in Thursday's New England Journal of Medicine.
Doctors test for anemia by measuring the percentage of oxygen-carrying red cells in the blood. Typically, patients are considered to have anemia if red cells make up less than 39 percent of their total blood.
The latest study found doctors should give transfusions if heart attack victims' readings are below 33 percent. In their study, 10 percent of patients had percentages this low.
In general, they found that the greater patients' anemia, the more likely they are to get transfusions, but many doctors treat only relatively severe cases. Overall, about one-quarter of those with readings under 33 percent got extra blood.
However, doctors need to be careful not to administer blood needlessly. The study raised the possibility that giving transfusions to those with levels over 36 percent might actually be harmful.
"A substantial number of lives may be saved when transfusions are administered to patients" with heart attacks who have red cell levels below 33 percent, concluded an editorial by Drs. Lawrence Goodnough and Richard Bach of Washington University.
Because the study did not set out to test the effects of transfusions, it is not considered absolute proof that treating anemia saves lives after heart attacks. But doctors say no such study is likely, and this is the best evidence available.
"I suspect that clinicians caring for elderly patients with heart attacks will incorporate these data into their practice," said Dr. David Meyerson of Johns Hopkins University.
Healthy people can usually tolerate anemia with little ill effect. However, during a heart attack, the heart muscle is starved of oxygen, and oxygen-poor blood appears to worsen the situation.
Krumholz said doctors should probably give the blood as soon as possible after a heart attack. However, some conditions, such as congestive heart failure, may make transfusions difficult.
Medical Editor Daniel Q. Haney is a special correspondent for The Associated Press.
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