Unconjugated bilirubin is a waste product formed during the breakdown of old red blood cells. It must undergo conjugation to become water-soluble and be excreted safely. Elevated levels can cause jaundice and require a blood test to diagnose.
Unconjugated bilirubin is the unrefined or crude bilirubin present in the body. Sometimes called free bilirubin or indirect bilirubin, it is a waste product that results from the process used to break down old red blood cells. Unconjugated bilirubin can be dangerous if the body becomes unable to process and excrete it.
Bilirubin is formed during hemolysis, a process in which the body naturally breaks down some red blood cells and will be replaced with new ones. After its formation, unconjugated bilirubin binds to a protein in the blood called albumin to travel to the liver. In this phase the bilirubin cannot be dissolved in water. Unconjugated or free bilirubin must undergo a process called conjugation before the body can finish getting rid of it.
The conjugation process transforms the unconjugated bilirubin into a water-soluble pigment. At this point, it becomes a component of bile – an essential digestive fluid – giving bile its yellowish color. It is stored in the gallbladder and used to help digest food. This allows the bilirubin to be safely excreted from the body during the digestive process.
Sometimes, however, unconjugated bilirubin can become problematic for the body. Some drugs have a tendency to suppress the liver’s ability to conjugate bilirubin. This can allow bilirubin to build up in the blood. There are also some diseases that can cause bilirubin to build up, including liver and blood disorders and blockages of the bile ducts. Symptoms of a buildup of unconjugated bilirubin in the blood include nausea, vomiting, and fatigue. It can also sometimes cause yellowing of the whites of the eyes or skin, called jaundice.
Laboratory tests are usually needed to determine if a patient has elevated levels of unconjugated bilirubin. Urinalysis alone is usually not sufficient testing for this purpose because urine normally contains a small amount of conjugated bilirubin. Consequently, bilirubin tests are conducted by drawing and testing a blood sample.
Doctors sometimes use a test called a “van den Bergh reaction test” to establish bilirubin levels. To perform this test, a small amount of blood must be drawn. The red blood cells are separated from the blood fluid, known as serum, and the serum is then diluted. By introducing a chemical into diluted serum and observing a reaction, a healthcare professional can assess whether the blood includes normal or elevated levels of bilirubin.
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