In AB phenotype, what would forward typing pattern show?

• A. Anti-A positive; Anti-B positive; A cells positive; B cells positive
• B. Anti-A negative; Anti-B positive; A cells negative; B cells positive
• C. Anti-A positive; Anti-B negative; A cells positive; B cells negative
• D. Anti-A negative; Anti-B negative; A cells negative; B cells negative

Answer: (A)

Forward typing checks which A and B antigens are present on a person's red blood cells by testing the cells with Anti-A and Anti-B sera. In an AB phenotype, red cells carry both A and B antigens. So the Anti-A serum will cause agglutination of the patient’s cells (A antigen present), and the Anti-B serum will also cause agglutination (B antigen present). This mirrors in the results as Anti-A positive and Anti-B positive, with A cells positive and B cells positive. If only one antigen were present, you’d see a positive reaction for that antigen and a negative one for the other; if neither antigen were present (type O), both would be negative.