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Bilirubin - Conjugated Versus Unconjugated

Bilirubin Lab Tests

When patients are extremely jaundiced, one of the common lab tests that is performed is a bilirubin test. This measures the amount of bilirubin that is in the bloodstream. This is often drawn as part of a complete metabolic panel. 

What is Bilirubin?

Bilirubin is a yellow/brown substance that is found within bile.  It is the waste product produced from the break down of red blood cells. Bilirubin is processed through the liver prior to being removed from the body. It is ultimately removed from the body in stool (which is why stool has the brown color that it does). 

There are two types of bilirubin that are found in the body: unconjugated and conjugated bilirubin.  Based on these values, you can figure out information about what the primary issue is causing abnormal bilirubin values. 

Unconjugated (indirect):  When the heme is released from hemoglobin (during red blood cell breakdown), the remainder is converted to unconjugated hemolgobin. This form of bilirubin travels from the bloodstream to the liver.  This molecule is not water soluble.

Conjugated (Direct):  Bilirubin is converted from unconjugated to conjugated bilirubin in the liver.  This happens when sugar attaches to the unconjugated bilirubin.  The unconjugated bilirubin turns into bile and enters the small intestines. It is eventually eliminated through a person's stool. This molecule is water soluble. 

Why Would It Be Elevated?

There are a variety of instances in which the bilirubin level may be elevated:

  • Liver failure: The liver is no longer doing its job and bilirubin is not converted from unconjugated to conjugated bilirubin (to then be excreted through stool).  The unconjugated bilirubin builds up in the body giving liver failure patients their yellow glow. 
  • Hemolytic anemia: Some patients have a rapid destruction of red blood cells.  Their bodies cannot keep up with this breakdown and the patient becomes jaundiced as a result.
  • Blockage of bile ducts: The bilirubin is not able to be excreted through bile into the small intestine and has increased numbers because of this physical obstruction.

If the unconjugated bilirubin levels are higher than the conjugated bilirubin, this could be caused by hemolytic or pernicious anemia, transfusion reactions, and cirrhosis. 

If the conjugated bilirubin levels are higher than the unconjugated bilirubin, this is typically due to a malfunction of the liver cells in conjugating the bilirubin.  This is commonly seen with drug reactions, hepatitis, as well as any type of liver disease.  This can also been seen due to some sort of blockage of the bile ducts.  Causes include gall stones, tumors, or scarring of the bile ducts. 

Nursing Tip: Conjugated bilirubin is water soluble.  If there is some sort of blockage of the bile ducts, excess conjugated bilirubin can be removed from the body through urine.  This is why bilirubin is tested for in the standard urinalysis. 


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This guest blog post by Courtney Tracy first appeared in From New To ICU.

Courtney is an experienced ICU nurse and the creator of From New to ICU. She enjoys helping nurses at all stages of their careers, from getting into nursing school, learning new skills or even searching for their first nursing job! Follow the links to learn and read more from Courtney.

Courtney is one of the members of our Affiliate Program, you may see our continuing education courses on her site From New to ICU. To support From New to ICU click on the course title of interest from the blog link. 

Posted: 6/21/2017 9:09:23 AM
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