An ABO typing result shows Anti-A: 0, Anti-B: mf, A cells: +, B cell: 0. Which B phenotype is most likely?

An ABO typing result shows Anti-A: 0, Anti-B: mf, A cells: +, B cell: 0. Which B phenotype is most likely?

• A. Bx
• B. Bm
• C. Bel
• D. B3

Answer: (D)

The pattern shows a B-type individual with a B antigen that is not expressed uniformly. Mixed-field reactivity with anti-B is a hallmark of the B3 phenotype, which is a partial or mosaic B antigen. In this case, A cells reacting and B cells not reacting align with a type B serum profile, and the mf result with anti-B points to partial B expression. Among the B subtypes, B3 is the classic example producing mixed-field agglutination with anti-B. The other subtypes (Bx, Bel, Bm) don’t fit the mf pattern as cleanly as B3, making B3 the best match.

The pattern shows a B-type individual with a B antigen that is not expressed uniformly. Mixed-field reactivity with anti-B is a hallmark of the B3 phenotype, which is a partial or mosaic B antigen. In this case, A cells reacting and B cells not reacting align with a type B serum profile, and the mf result with anti-B points to partial B expression. Among the B subtypes, B3 is the classic example producing mixed-field agglutination with anti-B. The other subtypes (Bx, Bel, Bm) don’t fit the mf pattern as cleanly as B3, making B3 the best match.