What Is Bilirubin?

A Byproduct of Breaking Down Red Blood Cells Involved in Digestion

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Bilirubin is a brown and yellow fluid that’s a byproduct of the essential process of the breakdown of red blood cells (RBCs). This substance is a major component of bile, an important digestive fluid that’s cleaned from the blood by the liver.

If the liver is damaged, bilirubin may leak into the bloodstream, which can lead to jaundice, characterized by a yellowing of the skin and eyes, among other symptoms. As such, the bilirubin test, which measures these levels, helps healthcare providers screen for diseases affecting the liver.

A doctor holding a test tube and figure of a liver

Shidlovski / Getty Images

Bilirubin in the Body

One of the major functions of the liver is to break down old or damaged RBCs, and, in this process, bilirubin is produced. In turn, this substance is combined with others to make up bile, an essential fluid for digestion.

Created in the liver and stored in the gallbladder, bile is released into the small intestine, where it helps break down fats from food. In healthy people, this liquid exits the body in urine and stool (feces), giving the latter its brown color. 

There are two forms of bilirubin observed in the bloodstream. Here’s a quick breakdown of each type:

  • Indirect bilirubin: This form is insoluble, meaning it will not dissolve in water. It travels to the liver via the bloodstream, where it’s converted to direct bilirubin, a water-soluble form.
  • Direct bilirubin: This is the form bilirubin takes once it’s been processed in the liver.

Both forms of bilirubin—as well as total levels—are measured to help determine health status. Generally speaking, higher levels of this substance in the body are evidence of problems with liver disease (such as hepatitis), blood disorders, as well as blockages of bile ducts (the tubes that connect the liver to the small intestines).       

Elevated Bilirubin Levels

Since the presence of excessive bilirubin in the bloodstream—a condition called hyperbilirubinemia—can mean significant health problems, it’s important to know the signs of this condition. The most significant is jaundice, which can be a hallmark of a range of other diseases of the liver and gallbladder.

What happens when you have hyperbilirubinemia? Here’s a quick breakdown of major symptoms:

  • Yellowing of skin and eyes
  • Fever
  • Darkened or brown-colored urine
  • Pale, lighter stools
  • Fatigue
  • Loss of appetite
  • Abdominal pain
  • Heartburn
  • Constipation
  • Bloating
  • Nausea/vomiting

Associated Conditions

High bilirubin levels and jaundice are a hallmark of a wide variety of conditions, many of which can become dangerous or deadly if untreated. These include: 

  • Hepatitis, an inflammation of the liver, is the result of infection by one of the five types of hepatitis virus: hepatitis A (HAV), hepatitis B (HBV), hepatitis C (HCV), hepatitis D (HDV), and hepatitis E (HEV). It can also occur due to drug use, alcohol abuse, or autoimmune disorder.
  • Cirrhosis is a scarring of the liver associated with long-term damage due to hepatitis infection (usually HBV and HCV), excessive alcohol consumption, or substance abuse, among other causes.    
  • Hemolytic anemia is characterized by the body’s inability to produce enough RBCs. This occurs because cells are destroyed faster than they can be generated.
  • Gallstones are stones made of crystallized cholesterol formed in the gallbladder. Though highly treatable, these can lead to significant health problems.
  • Liver cancer, which is often associated with HBV and HCV, can be deadly and requires immediate medical attention.
  • Blockage of the bile ducts, the tubes that connect the liver to the small intestine, also raises bilirubin levels. Chronic cases can lead to chronic liver disease or life-threatening infection.
  • Alcohol-related liver disease arises due to excess consumption of alcohol. The Centers for Disease Control (CDC) defines this as more than one drink per day for women, and more than two for men.
  • Kernicterus, a form of brain damage, occurs when there are severe cases of jaundice in newborns. This condition can lead to developmental challenges, other health problems, and, in rare cases, death.

Bilirubin Blood Test

Given how essential proper levels of this substance are to health, it’s little wonder that healthcare providers often call for bilirubin tests. Not only will this be performed in cases of adult jaundice (or if certain problems are suspected) but newborns are also screened as a standard of practice.

This test will most often be given as part of a wider regimen of screening; it lets practitioners get a better sense of the scope and severity of disease progression.

The test itself is a laboratory evaluation of a sample of blood, so it's well-tolerated and risk-free. Aside from the pinch where the blood is being taken from your body—usually in the inner arm opposite the elbow—there’s no pain. Results aren’t immediate; it may take a couple of days to a week before your healthcare provider sees them. 

Assessing Results

From the sample, practitioners focus on two important measures—the amount of direct bilirubin in the blood as well as overall (total) level in the blood. Based on what they see, they determine whether levels are normal or abnormal.

What are they looking for? The healthy range is clinically defined as less than 0.3 milligrams per deciliter (mg/dL) of direct bilirubin, with total levels between 0.1 and 0.2 mg/dL of direct bilirubin. Levels that deviate from that are considered abnormal and signs of problems. In these cases, of course, healthcare providers will then need to talk to the patient about next steps.

A Word From Verywell

Clearly, bilirubin plays an essential role in your body as an integral part of the digestive system. It's a substance that, if nothing is wrong, is often taken for granted. The story is different for practitioners, however—this fluid can be an important barometer of health

Bilirubin tests, as part of a wider battery of screenings, are robust tools for diagnosis and analysis and essential components in the healthcare provider's toolkit. They’ve helped improve the outlook for a huge number of patients suffering from a wide range of potentially very dangerous conditions.          

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Cleveland Clinic. Bilirubin test: test details & results. 2018.

  2. Michigan Medicine, University of Michigan. Bilirubin. 2019. 

  3. Fargo MV, Grogan SP, Saguil A. Evaluation of jaundice in adults. Am Fam Physician. 2017;95(3):164-168.

  4. Centers for Disease Control. Facts about moderate drinking. 2020.

  5. U.S. National Library of Medicine, National Institutes of Health. Bilirubin blood test. 2020. 

By Mark Gurarie
Mark Gurarie is a freelance writer, editor, and adjunct lecturer of writing composition at George Washington University.