Which pattern represents an acquired B phenomenon in ABO blood grouping: Anti-A 4+, Anti-B 2+, A cells 0, B cells 4+?

Which pattern represents an acquired B phenomenon in ABO blood grouping: Anti-A 4+, Anti-B 2+, A cells 0, B cells 4+?

• A. Anti-A 4+, Anti-B 4+, A cells 0, B cells 2+
• B. Anti A 4+, Anti B 1+, A cells 4+, B cells 2+
• C. Anti-A 4+, Anti B 2+, A cells 0, B cells 4+
• D. Anti A 3+, Anti B 0, A cells 0, B cells 2+

Answer: (C)

Acquired B phenomenon occurs when red cells that are typed as A acquire a B-like antigen on their surface, usually due to enzymatic modification caused by certain bacteria or underlying disease. This changes how the cells react in serologic testing: they no longer show the expected A antigen, and they gain a B-like determinant that reacts with anti-B antibodies. In this pattern, the A-cell screen shows no reaction (A cells 0), meaning those cells no longer display the A antigen. At the same time, the B-cell reaction is strong (B cells 4+), reflecting the presence of B-like antigen on those cells. The serum titers show anti-A stronger than anti-B, which can occur in this scenario, but the crucial point is the loss of A antigen and gain of B antigen on cells that should be A-type. This combination is characteristic of an acquired B phenomenon, where forward typing becomes inconsistent with the organism’s true genotype due to newly expressed B antigen on A cells. Clinically, this can complicate ABO grouping and is often seen in patients with certain GI conditions or infections; resolving the underlying issue can lead to normalization of the pattern.

Acquired B phenomenon occurs when red cells that are typed as A acquire a B-like antigen on their surface, usually due to enzymatic modification caused by certain bacteria or underlying disease. This changes how the cells react in serologic testing: they no longer show the expected A antigen, and they gain a B-like determinant that reacts with anti-B antibodies.

In this pattern, the A-cell screen shows no reaction (A cells 0), meaning those cells no longer display the A antigen. At the same time, the B-cell reaction is strong (B cells 4+), reflecting the presence of B-like antigen on those cells. The serum titers show anti-A stronger than anti-B, which can occur in this scenario, but the crucial point is the loss of A antigen and gain of B antigen on cells that should be A-type. This combination is characteristic of an acquired B phenomenon, where forward typing becomes inconsistent with the organism’s true genotype due to newly expressed B antigen on A cells. Clinically, this can complicate ABO grouping and is often seen in patients with certain GI conditions or infections; resolving the underlying issue can lead to normalization of the pattern.