Total bilirubin

Total Bilirubin is a measure of the amount of bilirubin in the blood. It is an important parameter in diagnosing and monitoring various liver diseases, bile duct obstructions, and hemolytic anemia. Bilirubin is a yellow compound that occurs in the normal catabolic pathway that breaks down heme in red blood cells. The measurement of total bilirubin includes both unconjugated (indirect) bilirubin, which is not water-soluble, and conjugated (direct) bilirubin, which is water-soluble.

Overview

Bilirubin is produced during the breakdown of red blood cells. Specifically, heme, a component of hemoglobin, is converted into biliverdin and then reduced to bilirubin. This unconjugated bilirubin is transported in the bloodstream to the liver, where it is conjugated with glucuronic acid to become water-soluble. The conjugated bilirubin is then excreted in the bile and helps to give feces its characteristic color.

Elevated levels of total bilirubin can indicate several health issues. High levels of unconjugated bilirubin may suggest hemolysis (the breakdown of red blood cells), Gilbert's syndrome, or other conditions affecting the liver's ability to process bilirubin. Elevated levels of conjugated bilirubin may indicate problems with bile flow, such as cholestasis or bile duct obstruction.

Measurement

Total bilirubin is measured in the blood through a simple blood test. The test results are usually reported in milligrams per deciliter (mg/dL) or micromoles per liter (µmol/L). The normal range for total bilirubin is typically between 0.3 and 1.2 mg/dL (5.1 to 20.5 µmol/L), but these values can vary slightly depending on the laboratory performing the test.

Clinical Significance

Elevated total bilirubin levels can be a sign of several conditions:

• Hemolytic anemia - Increased destruction of red blood cells leads to elevated unconjugated bilirubin.
• Liver diseases such as hepatitis or cirrhosis can impair the liver's ability to conjugate and excrete bilirubin, leading to elevated levels.
• Bile duct obstruction - Obstructions in the bile duct can prevent the excretion of conjugated bilirubin, causing its levels to rise in the blood.
• Gilbert's syndrome - A genetic condition that impairs bilirubin processing, leading to mildly elevated bilirubin levels.

Treatment

The treatment for elevated total bilirubin levels depends on the underlying cause. For example, addressing liver disease or clearing a bile duct obstruction can help normalize bilirubin levels. In cases of hemolytic anemia, treating the underlying cause of red blood cell destruction is crucial. For individuals with Gilbert's syndrome, treatment is often not necessary unless symptoms are bothersome.

See Also

• Jaundice
• Liver function tests
• Hemoglobin
• Hepatitis
• Cirrhosis