Bilirubin is a yellow pigment that is created by the breakdown of old red blood cells in the body. It is removed from the body by the liver, processed, and excreted in the stool.
The measurement of bilirubin levels in the blood is an important diagnostic tool for many health conditions and included in Liver Function Test Panel, particularly those related to the liver and the blood.
There are two types of bilirubin that are typically measured: direct bilirubin and indirect bilirubin.
Direct Bilirubin
Direct bilirubin, also known as conjugated bilirubin, is the type of bilirubin that has been processed by the liver and is ready to be removed from the body1. It is water-soluble, which means it can be dissolved in water and excreted in the urine1. Direct bilirubin is like a package that is ready for delivery.
High levels of direct bilirubin in the blood can indicate a problem with the liver’s ability to process bilirubin, or a blockage in the bile ducts that prevents the bilirubin from being excreted. Conditions that can cause high levels of direct bilirubin include hepatitis, cirrhosis, and gallstones.
Indirect Bilirubin
Indirect bilirubin, also known as unconjugated bilirubin, is the type of bilirubin that has not yet been processed by the liver1. It is not water-soluble and is bound to a protein in the blood called albumin that helps carry it to the liver3. Indirect bilirubin is like raw material waiting to be processed.
High levels of indirect bilirubin can indicate that the body is breaking down red blood cells too quickly, or that the liver is not able to process the bilirubin quickly enough23. Conditions that can cause high levels of indirect bilirubin include hemolytic anemia, Gilbert’s syndrome, and Crigler-Najjar syndrome.
What is differences between Direct bilirubin and indirect bilirubin?
Direct and indirect bilirubin play different roles in the body and provide different information about the body’s health. Direct bilirubin is a measure of the liver’s ability to process and excrete bilirubin, while indirect bilirubin is a measure of the amount of bilirubin being produced by the breakdown of red blood cells.
Both types of bilirubin can be measured in the blood, and the total bilirubin level is the sum of the direct and indirect bilirubin levels. However, the normal ranges for direct and indirect bilirubin can vary, and it is possible for one type of bilirubin to be high while the other is normal.
Examples of bilirubin test results:
Example 1: A healthy adult has a total bilirubin level of 0.8 mg/dL. This falls within the typical range for adults, which is less than 1.2 mg/dL.
Example 2: A newborn baby has a total bilirubin level of 12 mg/dL. This is considered high for a newborn, as jaundice usually becomes visible at a level of 2 to 3 mg/dL.
Example 3: An adult patient with liver disease has a direct bilirubin level of 0.6 mg/dL. This is higher than the typical result for direct bilirubin, which is generally 0.3 mg/dL.
Example 4: A patient with hemolytic anemia, a condition where red blood cells are broken down too quickly, has an indirect bilirubin level of 2.0 mg/dL. This is higher than the typical result for indirect bilirubin, indicating that the body is producing bilirubin faster than the liver can process it.
A quick comparison of direct bilirubin vs. indirect bilirubin:
| Feature | Direct Bilirubin | Indirect Bilirubin |
|---|---|---|
| Medical name | Conjugated bilirubin | Unconjugated bilirubin |
| Where | Processed by the liver | Breakdown product of red blood cells |
| Solubility | Water-soluble | Fat-soluble (needs albumin to travel in blood) |
| Normal level | Lower (around 0.3 mg/dL) | Higher (around 0.2-0.8 mg/dL) |
| Meaning of high levels | Indicates liver or bile duct problems | May indicate increased red blood cell breakdown |
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