Men under 50 who received blood donated by women who have ever been pregnant showed an increased risk of death after the procedure, reports a study released today. The findings raise new questions, but could have serious and widespread health implications.

The increased risk was shown in more than 31,000 patients who received nearly 60,000 red blood cell transfusions, the Dutch doctors reported in the Journal of the American Medical Association.

“Among patients who received red blood cell transfusions, receipt of a transfusion from an ever-pregnant female donor, compared with a male donor, was associated with increased all-cause mortality among male recipients but not among female recipients,” they conclude.

The study tracked the patients who were given blood at six Dutch hospitals over the course of a decade, from 2005 to 2015. Eighty-eight percent of the recipients of the blood were male, while six percent were women who had ever been pregnant, and six percent were females who had never been pregnant.

About 13 percent of the patients (3,969) died after received a transfusion over that time.

The risk for men under 50 was 13 percent greater if the donor of the blood had ever been pregnant. The increase in mortality disappeared when women who had never been pregnant, or men, were the source of the blood, they report.

Notably, the death risk increase disappeared for men over the age of 50, regardless of who the donor was, they add.

The increase in death is related to transfusion-related acute lung injury, or TRALI, they report. One possible explanation of the worse outcomes could be antibody formation and the activation of heretofore-unknown immune cells in the younger men.

But the doctors point to limitations with the data conclusions thus far – and said more explorations of the phenomenon have to be undertaken.

“Further research is needed to replicate these findings, determine their clinical significant, and identify the underling mechanism,” they write. 

JAMA published an accompanying editorial which contends, if the results are replicated, the study could have far-reaching consequences.

“If the results… are confirmed, these findings would have major implications for the management of blood transfusions by blood banks and transfusing physicians,” they write.