Introduction Blood products from female donors have been associated with worse outcome after blood transfusions. We aimed to quantify the association of overall mortality with transfusions from female blood donors. Methods We performed a cohort study of all transfusion recipients during a 5-year period at the Leiden University Medical Center. Analyses were performed in a sub-cohort of recipients with all transfusions from donors of the same sex. Effects in male and female recipients were analysed both separately and averaged, for an overall estimate. Results Overall, when averaged over both male and female recipients, transfusions from female donors were not associated with increased mortality. However, in male recipients transfusions from female donors were positively associated with mortality, while in female recipients the association was reversed. The hazard ratio for mortality after sex-mismatched transfusions was 1·2 (95% CI, 0·98–1·4). In recipients aged 1–55 it was 1·8 (95% CI, 1·2–2·7). In recipients over 55, with more other risk factors for mortality, it was 1·0 (95% CI, 0·83–1·2). Conclusions Overall transfusions from female donors were not associated with increased mortality. However, male recipients of blood from female donors did have an increased risk of death. Female recipients of blood from male donors showed a weaker increase in mortality.
