Pre-transfusion Testing Using Crossmatching Agglutination Reaction Grades Combined With Rh Subgroup Phenotyping in Patients With Autoantibodies: A Three-year Experience at a Tertiary Hospital.

Background: The currently recommended pre-transfusion testing techniques for patients with autoantibodies are complex, time-consuming, and labor-intensive. Therefore, although the red blood cell (RBC) selection method using crossmatched RBC agglutination reaction grades (i.e., the "least incompatible" transfusion) is discouraged, many institutions still use it. We aimed to evaluate the effectiveness of this method combined with Rh subgroup phenotyping.

Methods: We retrospectively investigated RBC transfusions from January 2019 to December 2021 in patients presenting as auto-control-positive via antibody identification (auto-control (+) group), where Rh subgroup phenotype-matched RBCs were selected based on the agglutination reaction grades of crossmatched units. For each study patient, an auto-control-negative patient was matched based on age, sex, department, and pre-transfusion Hb levels (auto-control (-) group). The mean Hb change per unit, transfusion-associated symptom/sign reports, and agglutination reaction grades upon crossmatching were analyzed.

Results: In the auto-control (+) group, the Hb change per unit among different agglutination reaction grades of transfused RBCs and among different relative grades of transfused RBCs and crossmatching auto-controls was not significantly different (P=0.392 and P= 0.132, respectively). No significant difference was observed in Hb changes and transfusion-associated symptom/sign occurrence between the auto-control (+) and auto-control (-) groups (P=0.121 and P=0.822, respectively). In addition, no definite evidence of hemolysis in the auto-control (+) group was observed in the medical record review.

Conclusions: Together with Rh subgroup phenotyping, selecting the RBC unit with the lowest agglutination reaction grade upon crossmatching does not adversely affect transfusion efficiency.