Exposure To ABO Compatible But Non-Group Identical Blood and In-Hospital Mortality

Transfusions that are ABO compatible but not group identical (mismatched) are given for a variety of reasons including inventory availability, avoiding wastage from outdating, and clinical urgency. A recent observation at our centre suggested that patient outcome was different for those patients that received a transfusion of units with a compatible but mismatched ABO group compared to those receiving ABO group identical blood. Hence, we performed a retrospective hospital registry study to explore the association between mismatched blood and in-hospital mortality in transfused patients.

Our patient/blood utilization database included 35,487 transfused hospitalized patients from 3 acute care academic centres from April 1, 2002 to October 31, 2011. Information on transfused RBCs included duration of storage (days) and ABO type. Patient data included: sex; age; hemoglobin; creatinine; diagnosis; interventions; ABO blood group and hospital discharge status. Factors associated with mismatched blood and in-hospital mortality were examined using generalized estimating equations to account for the potential serial dependence over multiple transfusions. The effect of exposure to ABO mismatched blood on in-hospital death was examined through Cox regression with time-dependent strata defined by: year of first admission; disease group; and the cumulative number of units transfused (≤ 7 days of storage; > 7 days but ≤ 28 days storage; and, >28 days of storage); and, controlling for available baseline and time-varying characteristics.

18,843 patients (blood groups A, B and AB), with complete covariates contributed to the analysis. Factors associated with transfusion of mismatched blood included: younger patient age (p<0.0001); lower hemoglobin (p<0.0001); higher creatinine (p<0.0001); intervention during hospitalization (OR=4.6, p<0.0001); and, patient ABO group whereby blood types A and B were much less likely to receive a mismatched unit compared to type AB patients (p<0.0001). There was a statistically significant interaction between patient blood type and the effect of receiving mismatched blood (p=0.034) with type A patients incurring a 79% higher risk of death (RR=1.79, 95% CI: 1.20, 2.67; p=0.0047); other patient blood types did not suggest increased risk. Similar results were observed when suspected trauma patients (≥ 6 units within 24 hours) were excluded from the analysis (Table 1).

Controlling for known potential confounders through Cox regression yielded evidence of increased risk of in-hospital mortality among blood type A patients receiving group O red cells. This association remained after suspected trauma patients were excluded from the analyses. Further study of the association observed in this study is warranted.

Cook:CIHR: Research Funding. Heddle:CIHR: Research Funding; Canadian Blood Services: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Health Canada: Research Funding. Eikelboom:CIHR: Research Funding.