Blood transfusions from women who have been pregnant may be lethal to men, study suggests

Male hospital patients receiving blood are more likely to die if they receive transfusions from a woman donor who has been pregnant, a new study suggests.

Researchers believe that antibodies acquired by women during pregnancy to protect the baby may trigger reactions in men which could prove fatal.

The most common cause of death was transfusion-related acute lung injury (Trali). Although the scientists warn that more studies are needed to replicate the findings, they say the results ‘if true, have significant clinical implications.’

Around two million blood transfusions are given in Britain each year and recipients are not told if their donor was a man or a woman.

Writing in the Journal of the American Medical Association, Dr Rutger Middelburg, from Sanquin Research in Leiden, and colleagues said: “Male recipients who received a transfusion from an ever-pregnant female donor had a statistically significant increase in mortality compared with those who received a transfusion from a male donor or from a female donor without a history of pregnancy.

“The association of increased mortality among male patients who received transfusions from ever-pregnant donors suggests a possible mechanism based on immunologic changes occurring during pregnancy.

“An alternative explanation could be a difference in iron status between ever-pregnant female and male donors. Some studies also report differences in red blood cell physiology between the sexes.

“Further research is needed to replicate these findings, determine their clinical significance, and identify the underlying mechanism.”

The scientists analysed death rates among 31,118 patients who received 59,320 red blood cell transfusions at six Dutch hospitals between 2005 and 2015. In total, nearly 4,000 patients, or 13 per cent, died after being given blood.

From all the men contributing to 1,000 years-worth of study (person years), there were 101 deaths after transfusion from an ever-pregnant donor compared with 80 after receiving blood from a male donor.

Women donors who had never been pregnant were associated with only 78 male deaths per 1,000 person-years.

Commenting on the findings, statistician Professor Kevin McConway, from The Open University, pointed out that the increase in risk was "not huge".

He added: "This is an observational study, and it is always difficult to establish what causes what in such studies.

"Maybe there is some difference between men who received blood from women who had been pregnant, and men who had blood from other donors, that has nothing to do with the source of the blood they received.

"Even if the effect on mortality is real, all the data come from the population of the Netherlands, and things may work differently in populations with different genetic backgrounds.

"For all these reasons and others, it's important not to read too much into this study, and I don't think there is yet any real cause for men to be particularly concerned about this issue if they need a blood transplant. At least, I'm a man, and I wouldn't be concerned."

A spokesperson for NHS Blood and Transplant said: "As the authors of this study have made clear, further research is needed to determine if it’s finding have any clinical significance. Blood donations from all our donors are lifesaving, and we continue to encourage donations from women who have previously been pregnant."

"Blood donation is an anonymised process and patients who receive a transfusion are not given any information about the donor."