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Retired NBME 23 Answers

nbme23/Block 3/Question#25 (reveal difficulty score)
A 43-year-old woman undergoing chemotherapy ...
Preformed IgM antibodies ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—yotsubato(1208)
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Transfusion reactions are mediated by Type II hypersensitivity reactions. These occur due to preformed antibodies that bind to the foreign antigen (AB group on RBC) and lead to hemolysis by NK cells. This is a form of Antibody dependent cellular cytotoxicity.

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focus  Exactly! And among the blood transfusion reactions, per FirstAid: allergic/anaphylactic reaction: type 1 (we would see urticaria, wheezing, etc. Seen in IgA deficiency.) febrile nonhemolytic transfusion reaction: type 2 (host antibodies against donor HLA and WBCs) acute hemolytic transfusion reaction: type 2 (ABO blood incompatibility) TRALI: its separate category (donor antibodies against recipient neutrophils and endothelial cells) They specifically told us ABO incompatibility (despite the respiratory symptoms that could indicate TRALI) so we know this is an acute hemolytic transfusion reaction. +2



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submitted by axsa19(9)
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AB is the only blood group that does not have preformed IgM antibodies in the plasma.

Blood group A has anti-B IgM

Blood group B has ani-A IgM

Blood group AB "NADA"

Blood group O has both anti-A & anti-B IgM

FA 2017 page 390

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axsa19  anti* +
noname  FA 2018 page 400 +
vulcania  FA 2019 p. 397 +1
destinyschild  blood group O also has IgG, which is significant bc it can cross the placenta and cause hemolytic anemia in a fetus +4



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