Old blood and female blood

Two recent studies caught my eye, both about blood transfusion.

The first study was published in NEJM by Cooper DJ, McQuilten ZK, Nichol A et el comparing use of freshest vs oldest available blood in critically ill patients. 

In this international, multi center, randomized, double-blind trial, critically ill adults were assigned to receive either the freshest available, compatible, allogeneic red cells (short-term storage group) or standard-issue (oldest available), compatible, allogeneic red cells (long-term storage group). The primary outcome was 90-day mortality.

Among the 2457 patients in the short-term storage group, the mean storage duration was 11.8 days. Among the 2462 patients in the long-term storage group, the mean storage duration was 22.4 days. At 90 days, there were 610 deaths (24.8%) in the short-term storage group and 594 (24.1%) in the long-term storage group (absolute risk difference, 0.7 percentage points; 95% confidence interval [CI], -1.7 to 3.1; P=0.57).

In other interesting study, published by Camila Caram-Deelder , Aukje L. Kreuger et el in JAMA.

In this cohort study conducted in 6 Dutch hospitals, that included 31 118 patients who received red blood cell transfusions, receipt of a transfusion from an ever-pregnant female donor was associated with a statistically significant increase in all-cause mortality among male recipients of red blood cell transfusions (hazard ratio, 1.13) but not among female recipients (hazard ratio, 0.99).

As with any cohort studies, it may be a pointer towards a causation but needs to be investigated further with more studies. Furthermore, if it stands true, we need to understand the mechanism.