ABO incompatible blood transfusions and increased in-hospital mortality in patients with group A blood

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A large multihospital registry (Transfusion Registry for Utilization Surveillance, and Tracking) was used to determine the association between exposure to ABO-nonidentical blood and in-hospital mortality. Data from 18,843 non-group O patients admitted between 2002 and 2011 and receiving at least 1 unit of blood were analyzed. Overall, group A patients had significantly increased risk of in-hospital death upon receiving non-identical unit (RR, 1.79; 95% CI, 1.20-2.67, p=0.005). There was no evidence of increased risk for group B or AB patients. Similar results were seen when only patients with circulatory disorders were considered. When patients with injury or poisoning were excluded, both group A and B patients had significantly increased risk of in-hospital death.
Alerting signals, symptoms, evidence of occurrence: 
The strength of this study is the way ABO-nonidentical transfusion is classified. Cox regression analyses controlled for sex, age, hemoglobin, creatinine, and in-hospital interventions and stratified by age of blood and admission year. The analyses also used a time-dependent nonidentical transfusion indicator that "switched on" as soon as an ABO-nonidentical unit of blood was transfused. By the other hand a methodologic limitation of the investigation is that it is a retrospective cohort study with many potential confounding variables. Patients included were admitted to and discharged from an acute care facility at the hospital between April 1, 2002, and October 31, 2011 and received at least 1 unit of blood. When patients had multiple hospital admissions during the study period, data only from the first admission were included. All patients were followed for the duration of their hospitalization (median, 8 days; mean, 14 days).
Demonstration of imputability or root cause: 
The analysis of a large, multihospital registry demonstrates an association between nonidentical blood and in-hospital mortality in group A patients. These observations are present when trauma patients are removed from the analysis and when individuals with circulatory disease alone are analyzed. The excess mortality risk conferred by nonidentical blood appears to be small, but it is significant and, if real, would translate into substantial impact at the population level. However, it is unclear why patients with blood group A would be affected differently by exposure to nonidentical blood, and further research is needed on the possible mechanism leading to explain this association.
Imputability grade: 
1 Possible
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Suggest references: 
Exposure to ABO-nonidentical blood associated with increased in-hospital mortality in patients with group A blood. Menaka Pai,Richard Cook, Rebecca Barty, John Eikelboom, Ker-Ai Lee, and Nancy Heddle. Transfusion. 2015 Oct 15. doi: 10.1111/trf.13376. [Epub ahead of print]
This paper is very intriguing and provocative… However, it is also 100% “statistics” and would need a review made by a specialist in statistics. At the same time the analysis seems to be very consistent. The confounding variables the authors have been able to find are controlled but other important variables could also explain these surprising findings. I am not totally convinced about the inclusion of this article into the Notify library. It might be premature...
Expert comments for publication: 
Other studies are necessary to confirm these findings and the potential mechanisms linking ABO-nonidentical blood with adverse outcomes. Confirmation of these data could pose a dilemma for blood supply and inventory management. At this time we can observe this intriguing association with caution. A complete switch to ABO-identical blood would be impractical and premature.