Men who receive a red blood cell transfusions have an increased risk of death if their donor is female and has been pregnant, a JAMA study suggests. 

No association was found for women who receive transfusions from ever-pregnant donors.

The research team from Sanquin Research, Leiden, in the Netherlands say their findings suggest a possible mechanism based on immunologic changes occurring during pregnancy.

But they note that further research was needed to replicate their findings and tease out any clinical significance.

The research team 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.

For male recipients of red blood cell transfusions, all-cause mortality rates after a red blood cell transfusion from an ever-pregnant female donor vs male donor were 101 vs 80 deaths per 1,000 person-years.

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

An accompanying editorial  described the results as “provocative” and if true, may have significant clinical implications.

However, it advised that as other studies have reported conflicting results, “alternative explanations for the observed associations should be considered.”