Traditionally the sex of a blood donor has been considered irrelevant when giving a blood transfusion, but a compelling study is raising new concerns suggesting blood transfusions delivered to men using blood from previously pregnant women could increase their risk of dying in the years following the transfusion.

The study from a group of Dutch researchers looked at 31,118 patients who received blood transfusions and not only broke the data down by sex, but also by whether the female blood donors had ever been pregnant. Mortality rates over a three-year follow up period were consistent across all datasets except one.

Men who received a blood transfusion from a female donor who had previously been pregnant were one and half times more likely to die than if they had received a transfusion from a man, or a woman who had never been pregnant.

Interestingly these results were only identified in men under the age of 50. It seems if a man is over the age of 50 he is immune to whatever specific risk factor is present in the blood of a formerly pregnant female donor.

Needless to say this study is provocative and the authors do clearly note that "further research is needed to replicate these findings, determine their clinical significance, and identify the underlying mechanism."

Conflicting data has been published in recent years over whether blood transfusions between sexes carry any risk. Gustaf Edgren, who has co-written an editorial on this new research, recently published a large scale investigation into whether or not the sex and age of a blood donor has any impact on the survival rate of a patient receiving their blood. Edgren concluded that the age or sex of a donor has no relevance in the mortality outcome of a blood transfusion.

Edgren does admit that this new study could have significant clinical implications though. "If the results reported by Caram-Deelder et al are confirmed, these finding would have major implications for the management of blood transfusions by blood banks and transfusing physicians," he writes.

Henrik Bjursten, another scientist working in the field, published a study on nearly 10,000 patients in 2016 and concluded that sex mismatched blood transfusions did in fact increase mortality risk. Despite the current lack of comprehensive evidence Bjursten thinks we should already be sex matching blood transfusions.

"My personal opinion is yes … I would want to have it sex-matched," Bjursten said in a recent interview with Scientific American. "There are millions of lives at risk here. Do we want to take the risk or do we want to go the safe route and try to avoid the harm?"

The latest study is the first to examine the relevancy of a female blood donor's pregnancy history and it asks the fundamental question of what could potentially be causing this strange increased risk of mortality?

The authors of the study speculate a certain antibody formation that occurs during pregnancy could be what is triggering the increased mortality for men receiving transfused blood. Why this only affects men not women, and only those under 50, is still unexplained.

Ultimately more research needs to be done to verify this unexpected link before any major cause of concern should be raised. But perhaps the most interesting implication to come out of the research is the possibility that the biological differences between men and women are more fundamentally far reaching than anyone could have anticipated.

The study was published in the journal JAMA.

Source: JAMA