Bilirubin

1. Bilirubin
By Lovepreet Singh Grewal
A bilirubin test measures the levels of bilirubin in your blood. Bilirubin (bil-ih-ROO-bin) is a yellowish
pigment that is made during the breakdown of red blood cells. Bilirubin passes through the liver and is
eventually excreted out of the body.
Higher than usual levels of bilirubin may indicate different types of liver or bile duct problems.
Sometimes, higher bilirubin levels may be caused by an increased rate of destruction of red blood cells.
Why it's done
Bilirubin testing is usually one of a group of tests to check the health of your liver. Bilirubin
testing may be done to:
Investigate jaundice — a yellowing of the skin and eyes caused by high levels of bilirubin.
This test is commonly used to measure bilirubin levels in newborns with infant jaundice.
 Determine whether there might be blockage in your bile ducts, in either the liver or the
gallbladder.
 Help detect liver disease, particularly hepatitis, or monitor its progression.
 Help evaluate anemia caused by the destruction of red blood cells.
 Help follow how a treatment is working.
 Help evaluate a suspected drug toxicity.
Some common tests that might be done at the same time as bilirubin testing include:
 Liver function tests. Blood tests that measure certain enzymes or proteins in your
blood.
 Albumin and total protein. Levels of albumin — a protein made by the liver — and
total protein show how well your liver is making certain proteins. These proteins are
necessary for your body to fight infections and perform other functions.
 Complete blood count. This test measures several components and features of your
blood.
 Prothrombin time. This test measures the clotting time of plasma.
 Introduction
Jaundice refers to the yellow discolouration of the sclera and skin (Fig. 1)
that is due to hyperbilirubinaemia, occurring at bilirubin levels roughly greater than
50 µmol/L.
Figure 1 – Yellowing of the sclera

2. Pathophysiology
Jaundice results from high levels of bilirubin in the blood. Bilirubin is the normal
breakdown product from the catabolism of haem, and thus is formed from the
destruction of red blood cells.
Under normal circumstances, bilirubin undergoes conjugation within the liver,
making it water-soluble. It is then excreted via the bile into the GI tract, the majority
of which is egested in the faeces as urobilinogen and stercobilin (the metabolic
breakdown product of urobilingoen). Around 10% of urobilinogen is reabsorbed into
the bloodstream and excreted through the kidneys. Jaundice occurs when
this pathway is disrupted.
Figure 2 – Bilirubin is produced as a byproduct of haem metabolism
Types of Jaundice
There are three main types of jaundice: pre-hepatic, hepatocellular, and post-hepatic.
1. Pre-Hepatic
In pre-hepatic jaundice, there is excessive red cell breakdown which overwhelms the
liver’s ability to conjugate bilirubin. This causes an unconjugated hyperbilirubinaemia.
Any bilirubin that manages to become conjugated will be excreted normally, yet it is
the unconjugated bilirubin that remains in the blood stream to cause the jaundice.
2. Hepatocellular
In hepatocellular (or intrahepatic) jaundice, there is dysfunction of the hepatic cells.
The liver loses the ability to conjugate bilirubin, but in cases where it also may become cirrhotic,
it compresses the intra-hepatic portions of the biliary tree to cause a degree of obstruction.
This leads to both unconjugated and conjugated bilirubin in the blood, termed a ‘mixed
picture’.
3. Post-Hepatic

3. Post-hepatic jaundice refers to obstruction of biliary drainage. The bilirubin that is not
excreted will have been conjugated by the liver, hence the result is a conjugated hyperbilirubinaemia.
Pre-Hepatic Hepatocellular Post-Hepatic
 Haemolytic anaemia
 Gilbert’s syndrome
 Criggler-Najjar
syndrome
 Alcoholic liver disease
 Viral hepatitis
 Iatrogenic, e.g.
medication
 Hereditary
haemochromatosis
 Autoimmune hepatitis
 Primary biliary cirrhosis
or primary sclerosing
cholangitis
 Hepatocellular
carcinoma
 Intra-luminal causes,
such as gallstones
 Mural causes, such as
cholangiocarcinoma,
strictures, or drug-
induced cholestasis
 Extra-mural causes,
such as pancreatic
cancer or abdominal
masses (e.g.
lymphomas)
Table 1 – Potential Causes for Jaundice, divided into pre-hepatic,
hepatocellular, and post-hepatic