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NBME 23 Answers

nbme23/Block 3/Question#25

A 43-year-old woman undergoing chemotherapy for ...

Preformed IgM antibodies

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submitted by yotsubato(416),

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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submitted by axsa19(4),

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

axsa19  anti* +  
noname  FA 2018 page 400 +  

O type patients have preform IgG anti A anti B. Not IgM antibodies "Shortly after transfusion" raise up suspicion for anaphylaxis. no sign of hemolysis-> favor anaphylaxis due to IgA deficiency=> effector cell is Mast cells

eclipse  they have IgG and IgM +  
kpjk  if it had been anaphylaxis- there would have been urticaria and pruritis +