unconjugated unbound bilirubin

[kfish365]

First question on this forum...here goes.

I know that unconjugated bilirubin is not water-soluble and that it has not reached the liver yet to be conjugated with glucuronic acid. My question is, is unconjugated also considered unbound even though it's using albumin as a transporter to get to the liver? Or is there actually such a thing as unbound unconjugated bilirubin? And if there is, then is that what the definition of "free" bilirubin is?

[Esme12, ASN, BSN, RN]

I need to think about this one....anyone else?

[smf0903]

I seem to recall reading something about unbound unconjugated bilirubin when we discussed hyperbilirubinemia in babies. I'd have to look, but as I remember there were some studies that indicated the higher the unbound unconjugated bilirubin, the higher the risk for neurotoxicity. I'll have to see if I can find those studies...

I would think that anything that alters the bilirubin/albumin relationship could cause someone to have unbound unconjugated bilirubin--cirrhosis?? If liver is already crummy, then low albumin and impaired conjugation=unbound unconjugated bilirubin?

I am just thinking out loud...I could be totally off-base

[edmia, BSN, RN]

I suggest doing a search on YouTube for: MedCram

This is a series of very well explained patho concepts with visuals. I'm pretty sure they have a bilirubin one.

But the short answer is that conjugated and unconjugated have nothing to do with bound or unbound.

After red blood cell destruction, heme and globin are split. Heme is further broken down until you end up with bilirubin. This bilirubin in plasma binds to albumin and is now unconjugated, aka free, bilirubin and lipid soluble. This unconjugated bilirubin travels to the liver where it joins glucuronic acid and becomes conjugated (and water soluble).

And smf0903 is correct. The term unbound bilirubin is used when referring to newborn jaundice and has more to do with the excretion and the risk for neurological damage.

Here is a good article that describes the unbound unconjugated free bilirubin of the neonate:

Bilirubin encephalopathy