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Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

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1. In this retrospective analysis, there was a slight increase in male patient mortality per transfusion when receiving blood from an ever-pregnant donor compared to a male or never-pregnant female donor.

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2. This association seemed to be strongest for recipients under 50 years of age.

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Evidence Rating Level: 3 (Average)

Study Rundown:

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Transfusion-Related Lung Injury (TRALI) is the most common cause of mortality due to blood transfusions. Previous studies have found an association suggesting that recipients of blood from female donors have a higher risk of this reaction. In this retrospective cohort study, patients who had received blood exclusively from male, never-pregnant female, or ever-pregnant female donors were followed over time in terms of all-cause mortality. Though no association was found for female recipients, a very slight increase in the hazard ratio for male recipients receiving blood from ever-pregnant donors was found for all-cause mortality per transfusion. However, the actual number of mortalities per total number of patients was lower for the ever-pregnant donor group versus the male donor group for male recipients. Further analysis by age suggested that the increase in mortality per transfusion for male recipients receiving blood from ever-pregnant donors was largest for those under the age of 50.

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This study had a number of limitations that casts uncertainty on its conclusions. First, there was not a correction for multiple comparisons, and the effect size reported for significant associations was small. These small effect sizes and rather tenuous associations brings into question the clinical significance of these findings. In addition, it is unclear why the mortality rate per patient represents an association in the opposite direction as the hazard ratio per transfusion. In summary, this study was not convincing in its conclusions, and further investigation would need to uncover more convincing evidence before these conclusions should be considered as unequivocal.

In-Depth [retrospective cohort]:

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From 2005 to 2015, there were 31,118 patients from 6 Danish hospitals that received blood transfusions from either male, ever-pregnant female, or never-pregnant female donors, consisting of 59,320 transfusions. Though no significant associations between female recipients and any donor group were found, there was an increase in the hazard ratio for male donors receiving blood from ever-pregnant females when compared to those from male donors (HR 1.13; CI95 1.01 – 1.26; p = 0.03 uncorrected for multiple comparisons). In addition, an interaction between age and donor for males suggested that males below the age of 50 were particularly susceptible to mortality after receiving blood from an ever-pregnant female (p < 0.001). However, the mortality rate for males receiving blood from male donors was 1722 deaths per 12,212 patients (14.1%) versus 1873 deaths per 13,699 patients (13.7%).

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