Red blood cells carry oxygen in the blood. The oxygen is carried on a protein called hemoglobin. When hemoglobin breaks down, part of it is converted into the chemical bilirubin. The bilirubin travels in the blood to the liver where it is excreted into the intestines through the bile ducts. High bilirubin levels are caused by problems with red blood cells, the liver or the bile ducts.
Red Blood Cell Problems
Problems that cause the red blood cell to burst and release hemoglobin into the blood can cause high bilirubin levels. These problems may be due to issues with the red blood cell that a person is born with, or those that are acquired from the environment.
Inborn problems in the red blood cell may include dysfunction of hemoglobin as in sickle cell disease. In addition, problems with proteins will also make the red blood cells subject to breaking apart. Problems with structural proteins that help give the cell shape and strength make it fragile. Problems with enzymes that help chemical reactions occur in the cells can cause toxins to build up.
Examples of problems with red blood cells that are not inborn include infections such as malaria. Certain toxins such as nitrites, aniline dyes, or snake and spider venom can also break apart red blood cells. In the condition called autoimmune hemolytic anemia, the immune system attacks the red blood cells. In some diseases, the flow of blood across a surface shears apart the red blood cells. In aortic stenosis, a main valve in the heart becomes stiff and narrowed, and blood flowing across it can tear apart the cells.
Liver Problems
Since the liver helps metabolize bilirubin, problems with its function will cause bilirubin to build up. Liver disease can be caused by, for example, an acetaminophen overdose, infections such as hepatitis A, B or C, alcoholism or cancer. In addition, certain genetic disorders prevent the liver from properly metabolizing and excreting bilirubin. Examples include Crigler-Najjar syndrome and Gilbert's syndrome.
Bile Duct Problems
The liver secretes metabolised bilirubin into the bile duct system where it is passed in bile into the intestinal tract. Gallstones and cancer can both obstruct the bile ducts. In primary biliary cirrhosis, the bile ducts are slowly destroyed by inflammation, perhaps as part of an autoimmune disorder in which the immune system attacks the bile ducts.
References
- "Harrison's Principles of Internal Medicine"; Anthony S. Fauci; 2008
- MedlinePlus: Jaundice - yellow skin
- Mayo Clinic: Primary Biliary Cirrhosis
