A National Institutes of Health-supported study found that the type of transfusion approach used to support adults who developed anemia after a heart attack did not make a significant difference in their likelihood of having another heart attack or dying within 30 days. Participants in the trial were randomized to receive a red blood cell transfusion when their red blood cell counts were in a prespecified range of moderate anemia, which is considered a liberal approach, or when it was more severe, a restrictive approach.
However, the researchers found that some adults who received blood at an earlier stage appeared to have slightly better health outcomes. Researchers encourage a flexible, nuanced approach in making these transfusion decisions.
"We think these results suggest that a liberal transfusion strategy may be most prudent for some patients without introducing excess risks of harm," said Jeffrey L. Carson, M.D., a principal investigator of the study and a distinguished professor of medicine at Rutgers Robert Wood Johnson Medical School, New Brunswick, New Jersey.
The findings, which were published in the New England Journal of Medicine and presented at the American Heart Association's 2023 Scientific Sessions, emerged from the Myocardial Ischemia and Transfusion (MINT) trial, a five-year, phase 3, randomized controlled study that started in 2017 to assess differences between the two transfusion approaches. Data from more than 3,500 participants from 144 sites in six countries were included in this analysis.
An estimated 11-38% of people who have a heart attack develop anemia, a condition marked by a potentially life-threatening drop in hemoglobin, a protein in red blood cells. Until now, doctors have had little evidence to guide their decisions about when to start a blood transfusion.
Currently, if a person has a heart attack and their hemoglobin levels falls below 10 g/dL, such as with a sudden loss of blood, they may receive transfusions to bring their hemoglobin levels above 10 g/dL. This liberal approach can improve oxygen delivery to the heart and reduce risks for complications. However, replenishing red blood cells too early can increase risks for fluid retention, inflammation, and adverse outcomes, such as heart failure. This is why some physicians use a restrictive approach by waiting until hemoglobin levels fall below 7-8 g/dL -widely considered severe anemia - before starting transfusions.
In the current study, researchers found no statistically significant differences between the transfusion approaches based on the number of heart attacks and deaths, the study's primary outcomes. Additionally, neither approach introduced unnecessary risks for harm. Among 1,749 participants in the restrictive transfusion arm, 295, or 16.9%, experienced a heart attack or death, compared to 255, or 14.5%, of 1,755 participants in the liberal arm.
The researchers observed benefits with the liberal strategy when they examined results for two other outcomes - unplanned heart surgery and cardiac rehospitalization - in addition to heart attacks and death. Based on these measurements, the researchers found that 8.3% of adults in the liberal transfusion arm, compared to 9.9% in the restrictive arm, died during the 30-day follow-up period. About 17% of participants in the liberal arm, compared to 20% in the restrictive arm, experienced a major adverse event.
Throughout the 30 days, less than 1 unit of red blood cells was used per participant in the restrictive transfusion arm compared to 2.5 units in the liberal transfusion arm.
"The study answers immediate treatment questions, while serving as a catalyst for future research - such as investigating long-term outcomes among participants," said William P. Tonkins, Dr. P.H., J.D., a program officer in the Blood Epidemiology and Clinical Therapeutics branch at the National Heart, Lung, and Blood Institute (NHLBI).
MINT (NCT02981407) is funded by NHLBI through grants U01 HL133817 and U01HL132853.
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