What is the fundamental purpose of an antibody screen?

• A. Screen for alloantibodies other than ABO immunoglobulins
• B. Detect Rh antibodies exclusively
• C. Identify autoantibodies to red cells
• D. Confirm ABO compatibility

Answer: (A)

An antibody screen is used to reveal unexpected antibodies against red blood cell antigens, i.e., alloantibodies, that a patient may have formed after transfusion or pregnancy. The test uses screening cells that express a panel of non-ABO red cell antigens; if a patient’s plasma contains an antibody against one of these antigens, the indirect antiglobulin test will detect the reaction. This matters because even with compatible ABO typing, clinically significant antibodies to other red cell antigens can cause transfusion reactions or complicate crossmatching. If the screen is negative, you can proceed with crossmatching more confidently; if positive, you identify the antibody to determine its specificity and then select donor units lacking the corresponding antigen. The screen focuses on non-ABO alloantibodies, not ABO antibodies, and it is not the primary method for detecting autoantibodies, which require other approaches.