What is the purpose of performing a saline replacement test during an antibody screen?

The saline replacement test is performed during an antibody screen primarily to confirm true agglutination. This test helps differentiate between genuine agglutination caused by the binding of antibodies to specific antigens on red blood cells and pseudo-agglutination that may result from nonspecific interactions or other factors such as protein-mediated actions.

In true agglutination, the antibodies present will cause the red blood cells to clump together, signifying a specific immune response to antigens on the cell surface. The saline replacement test works by adding saline to the sample; if agglutination persists, it indicates that true agglutination has occurred due to the antibodies in the patient's serum interacting with antigens on the red blood cells. Conversely, if the agglutination disappears upon the addition of saline, it suggests that the observed clumping was not due to specific antibody-antigen interactions.

The purpose is not to determine the blood type, identify antibodies, or measure hemolytic activity, but rather to clarify the nature of the agglutination observed during the antibody screening process. This clarity is crucial in ensuring accurate blood transfusion compatibility and patient safety.