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NBME 22 Answers

nbme22/Block 2/Question#9 (39.0 difficulty score)
A 26-year-old woman develops hypotension and ...
Antibody, complement C5-9🔍
tags: immuno abo_incompatibility complement 

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submitted by mattnatomy(41),
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submitted by abhishek021196(50),

acute hemolytic transfusion reaction (AHTR), also called immediate hemolytic transfusion reaction, is a life-threatening reaction to receiving a blood transfusion. AHTRs occur within 24 hours of the transfusion and can be triggered by a few milliliters of blood. The reaction is triggered by pre-formed host antibodies destroying donor red blood cells. AHTR typically occurs when there is an ABO blood group incompatibility, and is most severe when type A donor blood is given to a type O recipient.Antibodies against A and B blood groups (isohemagglutinins) present in the recipient's blood destroy the donor red blood cells.They also activate the coagulation cascade (blood clotting system) via factor XII, which can lead to disseminated intravascular coagulation and kidney damage. Isohemagglutinins also activate the complement cascade via C3a and C5a, which then promote inflammatory cytokine release from white blood cells. These inflammatory cytokines include IL-1, IL-6, IL-8, and TNF-alpha, which cause symptoms of low blood pressure, fever, chest pain, nausea, vomiting, and wheezing

submitted by potato_for_brains(1),
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hsTi is uacet yhctlimeo tuinsnfoars eaocntri, I Type II SRH so ’sesh gofrinm teaodiibns atgaisn het BAO srupog on eth lbood .cells mtnpeCmleo si duinedc by noitas.ibed

kfratta1  But with hypotension in the stem I thought more of anaphylaxis due to IgA def. Why would a T2 HSR give you hypotension? +3  
2ndmedschool  I think the hemoglobinuria is the key. As I’m looking at it it seems that anaphylaxis would cause hypotension, urticaria, itching, wheezing. ABO incompatibility is the only one that mentions hemoglobinuria. +17  
hyperfukus  abo incompatibility and rh incompatibility with mom blood rxns are gonna TYPE 2 no matter what it looks like +  

submitted by brise(44),

Can anyone explain why complement C5-9 is listed?

drdoom  don't have the stem in front of me but the Fc “handle” of antibody allows for opsonization (by macrophages and other APCs) but more immediately it activates circulating complement -> terminating in the formation of the Membrane Attack Complex. MAC is great way to kill nonself intruders without having to wait for macrophages to mature or neutrophils to arrive. FAST ACTIN’ TANACTIN! +1  
brise  Thank you so much! +1