October 17, 2017

expert reaction to study looking at blood transfusions from previously-pregnant women and risk of death in men

Researchers, publishing in JAMA, aim to quantify the association between red blood cell transfusion from female donors with and without a history of pregnancy and mortality of red blood cell recipients.

Prof. Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“This is a well-conducted study using appropriate statistical methods on data from a large number of patients.  Why, then, you might ask, are the researchers asking for more research rather than, say, a change in the way blood donors are selected?  Actually there are good answers to that, given in the research report and the accompanying editorial.  I’ll mention just some of them.

“The increase in mortality in men who received blood from women who had been pregnant is not huge.  If there is a good biological reason for the difference, it is not yet understood, though the researchers do describe some possibilities.  There is evidence of a difference in mortality only in some age groups, not all.  Also, because the data were originally collected for other purposes, over a long period of time, and not for this study, some of the figures are missing and the chances of inaccuracy are higher.  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.  That may seem unlikely, but some recent previous publications looking at possible differences in mortality between patients receiving blood from male and female donors have suggested that any such observed differences may be due to this so-called ‘confounding’.  The researchers on this new study did take some statistical care to avoid confounding, but it is never possible to allow for all possible confounding statistically, as the researchers themselves point out.  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.”

* ‘Association of blood transfusion from female donors with and without a history of pregnancy with mortality among male and female transfusion recipients’ by Camila Caram-Deelder et al. published in JAMA on Tuesday 17 October 2017.

Declared interests

Prof. Kevin McConway: “I am about to become a member of the Science Media Centre Advisory Board.”