Final answer:
The antibody screening test performed alongside pretransfusion blood typing ensures that the recipient does not have antibodies against non-ABO or Rh blood antigens to guarantee a safe transfusion.
Step-by-step explanation:
The antibody screening test that is done along with pretransfusion blood typing is used to ensure that the recipient is not making antibodies against antigens outside the ABO or Rh systems. Pretransfusion testing involves verifying the blood type of both the donor unit and the patient using commercially prepared antibodies against the A, B, and Rh antigens. If the donor blood type is confirmed, as for example A-positive, it will agglutinate with the anti-A.
Since red blood cells have many antigens in addition to ABO and Rh, the antibody screen test is crucial for determining if the patient has any antibodies to other antigens, which is especially possible in women with multiple pregnancies or patients with multiple transfusions. Patient serum is tested against pooled type O red blood cells, and if agglutination occurs, it is essential to identify the antigen and ensure it's not present in the donor blood. The cross-match assay is a final check before transfusion to confirm there's no hemagglutination, indicating that the patient does not have antibodies against the donor red blood cells.