Unconjugated bilirubin is the unrefined or raw 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 that will be replaced with new ones. After its formation, unconjugated bilirubin binds itself to a protein in the blood called albumin to travel to the liver. At this stage the bilirubin cannot be dissolved in water. The unconjugated or free bilirubin must undergo a process called conjugation before the body can finish getting rid of it.
The process of conjugation turns unconjugated bilirubin into a water-soluble pigment. At this point, it becomes a component in bile — an essential digestive fluid — giving the bile its yellowish color. It is stored in the gallbladder and used to help digest food. This allows the bilirubin to be harmlessly excreted from the body in the course of the digestive process.
Sometimes, however, unconjugated bilirubin can become problematic for the body. Certain drugs have the tendency to suppress the liver's ability to conjugate bilirubin. This can allow the bilirubin to build up in the blood. There are some illnesses that can cause bilirubin to build up, as well, including liver and blood disorders, and bile ducts blockages. Symptoms of a build-up 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 generally necessary to determine whether a patient has high levels of unconjugated bilirubin. Urinalyses alone usually aren't sufficient tests for this purpose because urine normally contains a small amount of conjugated bilirubin. As a result, bilirubin tests are conducted by taking and testing a sample of blood.
Doctors sometimes use a test called the "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 fluid of the blood, known as serum, and the serum is then diluted. By introducing a chemical into the diluted serum and watching for a reaction, a healthcare professional can assess whether the blood includes normal or high levels of bilirubin.