Before we understand direct bilirubin and indirect bilirubin, it is necessary to know what bilirubin is. Bilirubin is a yellow pigment or a substance that is formed when the red blood cells at the end of their life are broken down. Normal lifespan of RBC is 120 days. Bilirubin that is formed is called indirect bilirubin.
Types of Bilirubin:
Bilirubin is described into two types; indirect bilirubin and direct bilirubin. Indirect bilirubin is unconjugated bilirubin while direct bilirubin is conjugated bilirubin.
Direct bilirubin is transported from the biliary system into the intestine. It gets metabolized by the bacteria present in the intestine and turns into stercobilinogen. It is then eliminated through stool. Minimal amount of direct bilirubin remain in the circulating blood in a normal person. However, when there is problem in the liver such as hepatitis, or obstruction of the bile duct from bile stone, direct bilirubin level rises in the blood. Elevated level of direct bilirubin is found in condition such as:
- Cirrhosis of liver
- Bile duct obstruction from gall stone or a cancerous growth.
- Viral Hepatitis
- Alcoholic Hepatitis.
- Drug induced cholestosis
- Scarring and stricture of the bile duct.
- Liver cancer
- Pancreatic cancer
- Inherited diseases such as Wilson’s disease.
- Sickle cell anemia.
Difference between indirect and direct bilirubin:
- Indirect bilirubin also known as uncojugated bilirubin is produced from the breakdown of red blood cells in the circulatory system in spleen, liver and slightly in bone marrow. Direct bilirubin is produced out of indirect bilirubin in the liver.
- In liver the Kupffer cells are involved in production of indirect bilirubin. Direct bilirubin is produced from hepatic cells.
- Indirect bilirubin is highly toxic where as direct bilirubin is less toxic.
- Excretion of indirect bilirubin cannot be done in its initial form. It has to pass through process that turns it into direct bilirubin. Direct bilirubin is excreted via bile into intestine and finally through stool.
- High indirect bilirubin can cause damage to nervous system. High direct bilirubin can lead to formation of bilirubin stones in gallbladder.
- High indirect bilirubin is because of massive destruction of red blood cells or hereditary disease such as gilbert’s disease, or due to over dose of any medication.