Excluding anti-D, which antibody is most likely involved in HDN?

• A. Anti-D
• B. Anti-C
• C. Anti-E
• D. Anti-Kell

Answer: (B)

Hemolytic disease of the newborn occurs when maternal IgG antibodies against fetal red cell antigens cross the placenta and destroy those cells. If we exclude anti-D, the non-D Rh antibodies that most commonly cause HDN among the options is anti-C. This antibody can cross the placenta and target the C antigen on fetal red cells, leading to hemolysis and fetal anemia. Anti-E can also cause HDN but tends to be milder, and anti-Kell can cause severe HDN too, though it is less frequent than anti-C in many settings. So anti-C is the best fit as the likely non-D Rh antibody involved in HDN in this context.