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Retired NBME Step 2 CK Form 7 Answers

step2ck_form7/Block 2/Question#34 (reveal difficulty score)
An 8-hour-old newborn develops jaundice and ...
Rh incompatibility ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
tags: peds inc

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submitted by โˆ—russnels(20)
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Why would this not be ABO incompatibility? Is Rh incompatibility just more common?

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boostcap23  Yes for newborns specifically Rh incompatibility is more likely and also much more severe (see pg 405 FA 2020). ABO incompatibility would produce only mild jaundice and is actually quite common. +2
mguan1993  in addition i took the description of baby being edematous to mean hydrops fetalis, which Rh incompatability is associated with +2



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submitted by โˆ—endochondral1(24)
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why could the answer not be G6PD (also unconjugated) Or abnormal synthesis (what does this one even refer to?)

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komodo  G6PD causes hemolysis in response to oxidative stress (infection, foods, meds, etc.) which seems unlikely in this case. It also is not as severe as this case. Abnormal synthesis refers to thalassemia or sickle cell. Sickle cell doesn't present at birth due to high HbF levels. Alpha thalassemia could cause hydrops as well but would likely present in utero, so would have been detected during the pregnancy. +
klebsiella  please stop linking to yourself step_prep5 +1



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submitted by โˆ—step_prep5(246)
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  • Newborn is found to have unconjugated hyperbilirubinemia with anemia (consistent with hemolytic anemia) and signs of volume overload (hepatosplenomegaly, edema), most consistent with Rh-hemolytic disease
  • Potential causes of anasarca or hydrops fetalis:ย Rh-hemolytic disease, parvovirus/CMV infection of mother, hemoglobin Barts disease (severe form of alpha thalassemia), etc.
  • Key idea:ย ABO incompatibility will not present with as severe of a presentation because majority of maternal antibodies against other AABO blood groups are IgM and do not readily cross the placenta (contrast with acquired Rh-targeting antibodies in Rh-negative mother who has been exposed to Rh-positive blood which are IgG and can easily cross the placenta)

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