What is the principle of the antibody screen procedure?

• A. Reagent plasma with patient red blood cells
• B. Donor serum with patient red blood cells
• C. Patient serum with reagent red blood cells
• D. Patient serum with donor plasma

Answer: (C)

The principle is to detect antibodies in the patient’s serum by exposing it to red blood cells that have known antigen expression. In an antibody screen, patient serum is incubated with reagent red blood cells. If the patient has antibodies against any of the antigens on those screening cells, the antibodies will bind to the cell surfaces. After incubation, an antiglobulin step is used to reveal this binding; if antibodies are present, the sensitized cells will agglutinate, indicating an alloantibody.

This setup specifically tests the patient’s antibodies against common red blood cell antigens, which is why using patient serum with reagent red blood cells is the correct approach. Using donor plasma, or swapping which component is tested, would focus on antibodies in donor plasma or on the wrong pairings and would not reliably reveal the patient’s alloantibodies.