(P-TS-32) Determining the Clinical Significance of Passive anti-A in Group O Platelets

Our facility transfuses non-ABO identical platelets to our patients due to inventory constraints. This includes giving O platelets to A and AB patients. To avoid the risk of transfusing O platelets with a high titer of anti-A, we implemented a screening process in 2015. This is to restrict O platelets with high titer anti-A (a titer value >1:200 at immediate spin) to be transfused only to O patients. Subsequently, we changed our hospital information system (HIS) in 2018 and our test build required a sample collected for each suspected transfusion reaction (STR). One consequence of this change is a polyspecific direct antiglobulin test (DAT) is performed on all STRs. There is additional follow-up testing (monospecific DATs and antibody elution) on any positive DAT. When the patient is transfused ABO-incompatible plasma products, the eluate is tested against A1 and B red blood cells to determine if any passive ABO antibodies are detected.

Study

Design/Methods:

Passive anti-A antibodies were identified in 16 patients due to a STR workup. Transfusion Medicine physicians determined the transfusion reaction type based on CDC National Health Safety Network Hemovigilance Transfusion guidelines. Of those 16 STRs, 6 were interpreted as acute hemolytic reactions. The remaining STRs were interpreted as follows: 5 febrile non hemolytic, 2 transfusion associated circulatory overload, 1 allergic, 1 was not related to the transfusion and 1 was deemed not a reaction at all.

Results/Findings:

Of the 6 acute hemolytic reactions, all patients had the same symptoms of rigors/shaking chills and an increase in blood pressure. 5 out of 6 patients had increase in temperature during the transfusion. Only 1 reaction had a definitive case definition, was considered severe and a definite imputability. The anti-A platelet titer was 128 at immediate spin and an AHG titer of >1024. The other 5 were designated non-severe.

Conclusions:

In conclusion, the patients’ need for platelet transfusions exceeds the inventory of ABO matched units. Since implementation of the HIS in 2018, 26,244 group O platelets were transfused. Of those, 6332 (24.1%) went to group A recipients and 670 (2.6%) went to type AB recipients. Due to the process change, detecting passive anti-A due to non-group O platelets was possible, with 6 acute hemolytic STR reported out of 7002 (0.08%) units transfused to type A and AB patients.  We will continue to monitor acute hemolytic transfusion reactions due to passive anti-A but consider our practice of defining a high titer value of >1:200 as appropriate given our low rate of hemolytic STR.