Which antibody system is commonly implicated in severe delayed hemolytic transfusion reactions?

• A. Kidd (Jk)
• B. Duffy (Fy)
• C. MNS
• D. Rh

Answer: (A)

Delayed hemolytic transfusion reactions occur when the immune system mounts a secondary antibody response to donor red cell antigens after a transfusion. The Kidd antibody system is especially likely to cause this kind of reaction because anti-Jka or anti-Jkb often exists at low or undetectable levels but can rapidly rise in titer after re-exposure. That anamnestic response leads to brisk destruction of donor cells days to weeks after transfusion, and these antibodies can produce significant hemolysis even though initial screens might miss them. Clinically, you see a fall in hemoglobin with a positive DAT for IgG, and sometimes hemoglobinuria. Although other systems like Duffy or MNS and Rh antibodies can cause transfusion reactions, Kidd antibodies are the classic culprits behind severe delayed hemolytic transfusion reactions.