NBME Free 120 Decreased activity of UDP glucuronosyltransferase (NBME Answers)

Retired NBME Free 120 Answers

free120/Block 2/Question#34 (reveal difficulty score)
A 12-year-old girl is brought to the ...
Decreased activity of UDP glucuronosyltransferase 🔍 / 📺 / 🌳 / 📖
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submitted by ashmash(4)

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Why can’t we assume that the patient with an elevated direct bilirubin does not have some sort of obstruction where the alkaline phosphatase would be elevated (or even dubin johnson syndrome)? I didn’t think of Gilbert disease despite the intermittent course because I tend to look at direct and total bilirubin levels first to see if the direct bilirubin is elevated which in this case was elevated.

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bwdc Few things. History always comes first. She also has even more indirect bili than direct. There’s also no other indication of obstruction clinically (such as pruritis), and you can’t infer an elevated lab value (alk phos) and rely on that in order to have everything come together. They have to give it to you. +10

morelife I saw this question on Gilbert’s and also put down increased ALP. I noticed the relapsing-remitting history. However, my thoughts were that a direct bilirubinemia is a false finding in Gilberts (since it is due to lower UDP enzyme activity), and would more likely indicate obstruction. As you said, you would consciously neglect this finding in favor of the history? For these specific NBME style questions -- you know, the wishy/washy ones -- would you follow the principle of “history first”? +1

bwdc @morelife, Plethora of evidence first. Here everything points in one direction except one small detail. If you were to make a list of pro/cons for each diagnosis using history, physical and objective data (labs, imaging, etc), the scales usually tip firmly in one direction. +3

wowo also, unless I'm mistaken, it's not a direct bilirubinemia - tbili is 3 and direct is 1, so unconjugated is 2. They're both elevated. Even with a decrease in function of the enzyme, it still works, so if unconj bili increases, you'll get somewhat of an increase of conjugated bili +2

kindcomet @wowo, that makes sense if the unconj bili is due to hemolysis but it doesn't make sense if pathophys is literally the conjugation step. I would have expected DECREASED conjugated bili, if anything. +3

sexymexican888 Also serum haptoglobin is normal, if it was a hemolytic anemia (intrinsic) it would be decreased +2

an1 All Uw resources have said that Gilbert is an unconjugated raise and A/S condition unless there is a stressor... +

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submitted by ∗bwdc(697)

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Intermittent hyperbilirubinemia/jaundice in an otherwise healthy individual is typical of Gilbert’s syndrome, which is caused by the decreased activity of UDP glucuronosyltransferase.

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+1 upvote downvote
submitted by ∗azibird(279)

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This patient has a mixed hyperbilirubinemia. How could Gilbert syndrome, cause direct bilirubin to increase? The syndrome is caused by mildly decreased UDP-glucuronosyltransferase conjugation and impaired bilirubin uptake. So there's absolutely no way it could increase direct bilirubin! I thought this must mean that there was an obstruction or extravascular hemolysis.

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+0 upvote downvote
submitted by ∗divinedomain(1)

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honestly fuck them. increased direct should point you to another dx.

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