Bilirubin, a yellow pigment formed during the breakdown of red blood cells, passes through the liver and is eventually expelled from the body.

Elevated bilirubin levels may suggest various liver or bile duct issues. Increased levels can also result from a higher rate of red blood cell breakdown.

What is Bilirubin?

Bilirubin is a waste product from old red blood cells. Normally, your body eliminates it through your intestines. Along the way, it might offer some benefits. Recent studies propose that it acts as an antioxidant, guarding against cardiovascular disease. However, excessive amounts can be harmful. 

Why is it tested?

Bilirubin testing is a part of a set of tests to assess liver health. It is performed to:

• Investigate jaundice, which is the yellowing of the skin and eyes due to high bilirubin levels. This test is commonly used in newborns with infant jaundice.
• Determine whether there might be a blockage in your bile ducts, either in the liver or the gallbladder.
• Detect liver disease, especially hepatitis, or monitor its progression.
• Evaluate anemia caused by the destruction of red blood cells.
• Monitor the effectiveness of a treatment.
• Assess suspected drug toxicity.

Liver Function Tests

Direct vs. indirect bilirubin (or conjugated vs. unconjugated)

Your liver processes bilirubin which arrives in an “unconjugated” form, meaning it’s not soluble in water. It’s attached to a blood protein called albumin, which aids in transporting it to your liver. During processing, the liver separates it from albumin and links it to a sugar molecule, making it water-soluble. This enables it to mix with bile and pass through your intestines.

The bilirubin your liver processes is referred to as “conjugated,” and on test results, it may be labeled as “direct” bilirubin. This type can be directly measured. In contrast, “unconjugated” bilirubin, which cannot be directly measured, is calculated by subtracting the value of conjugated bilirubin from the total bilirubin in your blood. Test results may label unconjugated bilirubin as “indirect.”

Results

The bilirubin test reveals results in terms of direct, indirect, or total bilirubin. Total bilirubin is a combination of direct and indirect bilirubin. Typically, results for direct and total bilirubin are provided. 

For adults, typical results for a total bilirubin test are 1.2 milligrams per deciliter (mg/dL), usually 1 mg/dL for those under 18. Direct bilirubin results are generally around 0.3 mg/dL.

These results may slightly differ between laboratories and may vary for women and children. Foods, medicines, or strenuous exercise can also impact results. Inform your healthcare provider about your activity levels and any foods or medicines you’ve consumed.

Bilirubin can accumulate in your blood if:

• Your body breaks down red blood cells too quickly. Overproduction of bilirubin may occur with a blood disorder like hemolytic anemia, which destroys red blood cells.
• Your liver is having difficulty processing its usual amount of bilirubin. The liver may struggle with occasional toxic overload or have a chronic liver disease affecting its function.
• Your biliary system isn’t efficiently clearing bile. A blockage in your bile ducts or gallbladder could cause bile to back up and leak into your bloodstream.

Low levels are typically not a cause for concern. Some medications, such as antibiotics, birth control pills, sleeping pills, and seizure medications, can reduce your bilirubin levels.

Summary

If you observe visible jaundice (yellowing of the skin and eyes), it’s a clear indication to consult a healthcare provider for a bilirubin test. Jaundice becomes apparent when bilirubin levels are two to three times the normal range. Darker or tea-colored urine may also be noticeable within this range. However, high bilirubin can exist without visible signs. A bilirubin test assists in confirming your provider’s suspicions about specific diseases and helps identify the underlying cause.

References:

1. (2022). Retrieved from https://www.mayoclinic.org/tests-procedures/bilirubin/about/pac-20393041 
2. (N.d.). Retrieved from https://www.mayocliniclabs.com/test-catalog/overview/8452 
3. professional, C. C. medical. (n.d.). Retrieved from https://my.clevelandclinic.org/health/diagnostics/17845-bilirubin