Selection of donor RBCs for a patient with auto anti-e, but who is E-negative and e-positive

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ADDENDA June 12, 2006

11. A transfusion medicine physician in Los Angeles (different than the respondent of ADDENDUM 4) reports that in a case such as the one under discussion, he would not be at all concerned about 'exposing' the patient to the E antigen, since, after all we do not routinely take this precaution for any other patients (with the exception of those with sickle cell disease) and simply live with the consequences of alloimmunization if it should occur. More importantly, however, it should be recognized that the 'e' specificity of autoantibodies is 'fake' - it is only an apparent specificity. This has been demonstrated many times by the ability of e-negative RBCs to absorb such antibodies to extinction, which would not be possible with true alloanti-e. Also, although there have been reports in the literature suggesting that e-negative RBCs have superior survival in these patients, other reports suggest the opposite. Therefore, it is his opinion that no good studies exist supporting the benefit of routinely utilizing e-negative RBCs for transfusion under these circumstances. Given the rarity of R2R2 units of blood and the possible delays in delivering needed transfusions when attempting to secure these units, his transfusion service has chosen to neglect the 'e' specificity of these autoantibodies when transfusing such patients.

ADDENDA June 20, 2006

12. A transfusion medicine physician in Vermont reports that at his hospital they do not routinely 'respect' the auto-anti-e unless there is evidence to suggest that it is contributing to hemolysis. If they were worried about the antibody and had no choice, they would transfuse e-positive units by "in vivo" crossmatch, which entails demonstrating lack of hemolysis after transfusing 30-50 cc of blood slowly and then checking for hemolysis again after the completion of the unit. This might not be easy to do in the case of a patient going to cardiac surgery however. Part of the decision to not respect the auto-anti-e is that they are not usually clinically significant and e-negative RBC units are only 2% of the inventory. Avoidance of the development of an anti-E was not in their calculation since 70% of units are E-negative. An alternative approach for the example given would be to give e-negative units first and then deal with the situation of anti-E if should develop afterwards. since E-negative units are not hard to find. What was not mentioned in the original case description that began this discussion was whether the patient was Rh positive or not. If the patient is Rh negative, then you're kind of stuck and you would not go out of your way to get e-negative units (r'' or r(y) cells are rather rare) unless there was clear evidence to suggest that the auto-anti-e caused more rapid destruction of e-positive cells than e-negative cells. The respondant would be more concerned about anti-D formation than he would be about anti-E formation, if the patient was Rh negative. For an Rh positive patient, he would have the luxury of choosing e-negative cells, if so inclined (R2R2).
    
    
13. A physician at an academic institution in Boston (different from the physician in addenda 1 or 2) reports that at her hospital, a scenario of an auto anti-e can be very complicated depending on the patient's current need for RBCs (emergent transfusion need or is there time for adsorption and other testing), the strength of the autoantibody (is the patient actively hemolyzing), recent and remote alloimmunizing events (e.g., pregnancies and transfusions), and finally the patient's perceived future transfusion needs (history of heme malignancy may suggest greater future transfusion needs). The scenario described an optimal timing situation, which allowed the physician who submitted the case description to obtain patient history and complete testing to rule out possible underlying alloantibodies and to phenotype the patient. Assuming the patient is not actively hemolyzing, it is probably in the patient's best interest to receive E-negative RBC units, such as R1R1 to prevent possible alloimmunization to the E-antigen (E-antigen is highly immunogenic, with D-, K-, and C-antigens being more immunogenic). If the patient is hemolyzing due to the auto anti-e, then R2R2 should be used to stabilize the patient, knowing that the patient will be at risk for developing an anti-E, and would then later require E-antigen negative RBCs.

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