Why are O group red cells commonly used for screening in antibody testing?

• A. They express A and B antigens
• B. They are universal donors for plasma
• C. They lack A and B antigens
• D. They carry high density of A and B antigens

Answer: (C)

The main idea is to avoid ABO interference when screening for antibodies. O group red cells lack A and B antigens on their surface, so they provide a neutral background. Any reaction seen during screening is then due to antibodies against other red cell antigens (like Rh, Kell, Duffy, etc.), not due to anti-A or anti-B antibodies that some patients naturally have. If cells with A or B antigens were used, anti-A or anti-B present in a type O patient's serum could react, confounding the result and making it harder to detect antibodies against non-ABO antigens. That’s why these cells are the best choice for screening.