In a randomized clinical trial with almost 9,000 patients, the adjusted hazard ratio 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.
“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, said in an interview. “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,” Dr. Fergusson added.
The study was published 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 Dr. Fergusson. “That itself would have downstream effects on the recipient.”
The current double-blind study included 8,719 patients who received transfusions from September 2018 to December 2020 at three academic medical centers in Canada. Of this group, 5,190 received male donor blood, and 3,529 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, 1,141 patients in the female donor group and 1,712 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 Dr. Fergusson. “But those differences really don’t matter in the recipient.”
The design of the trial itself was unique, Dr. 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. 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 to 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 20-29.9 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.