Step I billirubin question

Started by Dawg_MD
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Dawg_MD

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Could someone please remind me of the significance of elevated conjugated vs unconjugated billirubin levels? Does it just differentiate intravascular vs extravascular hemolysis?

Thanks
 
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What's the answer?

All I remember is that conjugated bilirubin is water soluble--hence excreted in the urine.

Enlighten me, please!
 
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unconjugated bilirubin=pre-hepatic, h2o insoluble, from hemolysis. if there is increased hemolysis (hemolytic anemias), or if the liver is not able to keep up with demands, unconjugated bili goes up. unconjugated bili crosses the blood-brain barrier and is neruotoxic.

conjugated bilirubin=post-hepatic water soluble. if the liver is conjugating all the bilirubin it recieves, but there is some sort of obstruction in the biliary tree (stones, tumor) then conjugated bilirubin backs up in the blood stream, so increase serum conjugated bilirubin. (this is also changed to urobillinogen, which can be seen in the pee at high levels of serum conjugated bili)

there is usually an increase in both with intra-hepatic problems, such as hepatitis and cirrhosis, as the liver is not effeciently conjugating or secreting the bilirubin.

so, diagnostically, the type of bilirubin in excess is important to help localize the problem.
 
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Hi Neilc,

Thanks for the explanation--I appreciate you taking the time to explain the mystery. Just wish I had known that for the Biochem test last year!!!!

Thanks again
 
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If you have some form of hemolytic anemia where the spleen is responsible for the destruction of RBC (extravascular), I do not believe you will see a rise in unconjugated bilirubin because the bilirubin is taken to the liver through the portal system for conjugation before it reaches systemic circulation. I guess if the liver gets overwhelmed you might see it though.
 
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it shouldn't matter where the rbc destruction occurs, as it all winds up in the liver: rbc degrades to heme, heme to biliverdin, biliverdin to unconjugated bilirubin, which than goes to the liver. so, if you have a hemolytic anemia, bilirubin (unconjugated) levels increase, no matter where the destruction occurs, because the liver cannot keep up with demand. you can also get the rise with no significant hemolysis if the liver has poor uptake of bilirubin and can't keep up with demand.


i got this question on my exam yesterday, and i knew it pretty well..but the friggin prof started asking me about structures! i don't know structures!!!!
 
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ahh...another first fac student? you know matous, loves those structures. but, i still got my 1.

who are you?
 
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