Direct Bilirubin

What is Direct Bilirubin?

Direct bilirubin, also called conjugated bilirubin, is the water-soluble form of bilirubin that has been processed by the liver. When red blood cells break down, they produce bilirubin, which the liver conjugates with glucuronic acid to make it easier to excrete in bile. Direct bilirubin specifically measures this liver-processed portion of total bilirubin.

Why is it Tested?

Direct bilirubin is measured to evaluate liver function and bile duct problems, particularly when total bilirubin is elevated or when symptoms suggest liver disease. It helps distinguish between liver-related causes of jaundice (high direct bilirubin) and blood-related causes (high indirect bilirubin). It’s especially useful for detecting bile duct obstructions and certain liver diseases.

Normal Ranges

What do Abnormal Results Mean?

Abnormal results are not a diagnosis. Always discuss your results with a qualified healthcare provider before making any medical decisions.

Low Direct Bilirubin

Low or undetectable levels are normal and indicate proper liver processing and bile excretion. This is the typical finding in healthy individuals.

High Direct Bilirubin

Elevated direct bilirubin suggests problems with bile flow or liver cell function and may indicate:

• Bile duct obstruction (gallstones, tumors)
• Hepatitis or other liver inflammation
• Primary biliary cholangitis
• Drug-induced liver injury
• Inherited disorders affecting bilirubin transport
• Sepsis or severe infection

How to Track Over Time

Monitoring direct bilirubin trends helps evaluate liver function and bile duct health over time. Rising levels may indicate developing obstruction or worsening liver disease, while decreasing levels often suggest improvement in liver function or resolution of bile duct problems. The direct-to-total bilirubin ratio provides additional diagnostic information.