Red-Cell Donor's Sex Does Not Affect Transfusion Survival

Richard Mark Kirkner

April 17, 2023

The sex of a red blood cell donor has no effect on the survival of a transfusion recipient, data suggest.

In a randomized clinical trial with almost 9000 patients, the adjusted hazard ratio (HR) of death among recipients of female donors' blood, compared with recipients of male donors' blood, was 0.98. The data contradict the finding of previous observational studies that donor sex is associated with recipient outcomes.

Dr Dean Fergusson

"The key finding was that we actually had a null result," study author Dean Fergusson, MD, PhD, senior scientist at the Ottawa Hospital Research Institute in Canada, told Medscape Medical News. "We went in thinking that male donor blood would confer a benefit over female donor blood, and we found that there's absolutely no difference between the donor sexes on recipient outcomes — mortality and other major secondary outcomes," Fergusson added.

The study was published April 13 in The New England Journal of Medicine.

Differences "Don't Matter"

A 2015 article from the National Heart, Lung, and Blood Institute identified a potential effect of donor sex on transfusion recipient survival. Since then, several observational studies have suggested that donor sex may influence survival after transfusion. This research includes two large studies, one from Canada and one from the Netherlands, that reported a heightened risk of death among recipients of red-cell units from female donors or donors who had been pregnant. Other studies, however, yielded conflicting results.

"The rationale was that female blood, because of biochemical properties, different hormones, exposure to babies and other males, all led to a different product, if you will, and these subtle changes could affect the blood product in terms of shelf life and potency," said Fergusson. "That itself would have downstream effects on the recipient."

The current double-blind study included 8719 patients who received transfusions from September 2018 through December 2020 at three academic medical centers in Canada. Of this group, 5190 received male donor blood, and 3529 received blood from female donors.

The researchers randomly assigned patients in a 60:40 ratio to male and female donor groups. Data collection and follow-up were performed by the Ottawa Hospital Data Warehouse, Canadian Blood Services, and ICES, an independent research institute. Patient characteristics were similar in both trial groups at baseline.

After an average follow-up of 11.2 months, with a maximum follow-up of 29 months, 1141 patients in the female donor group and 1712 in the male donor group died. The study found no statistically significant difference in overall survival between the two groups. The unadjusted HR for death, with the male group as the reference, was 0.97, and the adjusted HR was 0.98. The rates of overall survival were 58% and 56.1% in the female and male donor groups, respectively.

The study did not prove that differences in outcome based on donor sex do not exist, said Fergusson. "But those differences really don't matter in the recipient," he said.

The design of the trial itself was unique, Fergusson said. After patients consented to participate and underwent randomization, the study used routinely collected data from the participating hospitals' electronic medical records rather than collect data anew for each patient. "That had a profound effect on the efficiency of the trial," he said. "We did this trial for a cost of less than $300,000, and typically it would cost $9 million by using high-quality electronic health data."

The study also evaluated several secondary outcomes. Recipients of female donor blood had twice the incidence of MRSA infection. In addition, an unadjusted subgroup analysis suggested a 10% lower risk of death among male patients assigned to the female donor group, compared with those assigned the male donor group.

The risk of death was almost three times higher among patients in the female donor group who received units from donors aged 20 to 29.9 years (HR, 2.93). "The inconsistency of the point estimates across groups and the multiplicity of analyses increase the risk that those findings were due to chance," according to the authors.

Big Data

Commenting on the study for Medscape, Jeannie Callum, MD, professor and director of transfusion medicine at Queen's University School of Medicine in Kingston, Ontario, said that the use of routinely collected data from the participating hospitals' electronic medical records was "one of the really great things about this paper."

Dr Jeannie Callum

This use of Big Data "allows you to do a trial like this with almost 9000 patients without spending millions and millions of dollars to have people go through charts and record data," she added.

Callum also pointed out some of the trial's limitations. "One of the things that kind of detracts from the study in my mind is that they randomized everybody that was getting a transfusion, but outpatients getting a transfusion have a very low mortality rate. So, you have a group of patients that are never going to have that endpoint being included in the study, and that might've diluted the findings."

About 11.4% of participants received blood from a donor group other than the one to which they had been assigned, and this factor may further dilute the findings, said Callum. "That's a difficult thing to avoid." She noted that a trial in which she is collaborating, called Sex Matters, may answer some of these questions about the use of female vs male donor blood.

The investigators also noted that the findings may not be generalizable to other countries. "Just because we didn't find something in Canada with our blood production system doesn't mean that the United States might not find it different, because how they manufacture their red blood cells for transfusion is different than how we do them in Canada," said Callum.

Nonetheless, this study shows the potential of using Big Data in medicine. "This is the future of large randomized clinical trials to quickly answer questions," said Callum. "In the United States, Canada, and other countries that have these large electronic medical records systems, this kind of trial would be able to be done in other centers."

The study was funded by the Canadian Institutes of Health Research. Fergusson and Callum have disclosed no relevant financial relationships.

N Engl J Med. 2023;388:1386-1395. Abstract

Richard Mark Kirkner is a medical journalist based in the Philadelphia area.

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