Based on the following pattern, which antibody is suspected? Anti-A 4+, Anti-B 0, Anti-D 4+, A1 Cells 1+, B Cells 3+, SCI 3+, SCII 3+, SCIII 3+, Adult O cells 4+, Cord O cells 0.

• A. Anti-IH
• B. Anti-I
• C. Anti-D
• D. Anti-A1

Answer: (B)

The pattern points to an antibody against the I antigen on red cells. Anti-I is a cold agglutinin that binds to I antigen, which is present on most adult red cells but is sparse on cord blood cells (cord cells mainly carry i antigen). Because of this, you get strong agglutination with adult cells (including Adult O cells) and little to no reaction with cord cells, which matches the observed results: strong reactions with adult cells and zero with cord O cells. Other antibodies would produce different patterns (for example, anti-A1 would mainly react with A1 cells, and anti-D would correlate with D antigen presence rather than the I antigen pattern). So the findings best fit Anti-I.