Physiological Impact of Hyperbilirubinemia

Hyperbilirubinemia refers to the condition in which excessive levels of bilirubin is found in the blood. Bilirubin is the substance produced when old red blood cells are broken down, a process called hemolysis. Bilirubin is yellow in color, thus causing yellowing of the skin and eyes, a prominent feature of hyperbilirubinemia. The common term given to this yellowing is jaundice. Etiology, or causation, may be pre-hepatic, hepatic or post-hepatic.

Bilirubin Metabolism

• Under normal circumstances, bilirubin is taken up by the liver after it has been released into the blood. The liver then concentrates it, making it into bile. Bile leaves the liver via bile ducts, is stored in the gallbladder and excreted into the small intestine when needed. Bile helps emulsify fats and ranges from a green to yellow-brown color. Bilirubin is eventually excreted as stool. A small amount of bilirubin is also reabsorbed from the intestine back into the blood; it is taken up by the kidneys and becomes part of urine and is excreted.

Pre-Hepatic Jaundice

• Pre-hepatic jaundice is caused by pathology occurring in the blood, causing increased hemolysis. The body increases the formation of red blood cells in an effort to compensate for the increased rate of hemolysis. This results in an abnormally large number of young red blood cells in the blood. Pre-hepatic jaundice is characterized by paleness, light yellowing of the skin and eyes, and a decrease in red blood cells (anemia). The spleen may be enlarged. Although rare, this condition can have a genetic cause, referred to as genetic hyperbilirubinemia.

Hepatic Jaundice

• When jaundice is caused by failure of liver cell function or an obstruction within liver bile ducts, it is called hepatic jaundice. In liver cell failure, production of bilirubin is normal, but it accumulates in the blood causing hyperbilirubinemia. This may be caused by viral infection such as hepatitis, cirrhosis and cancer of the liver due to certain poisons, alcoholism and drugs. Hepatic jaundice can occur due to liver cell swelling which obstructs ducts within the liver preventing the normal flow of bile. It is typically caused by liver cell inflammation, trauma, infections and certain drugs. When jaundice is due to obstruction, it is called "intrahepatic obstructive jaundice."

Post-Hepatic Jaundice

• Jaundice may also be caused by bile flow obstruction occurring within the bile ducts (outside of the liver). Typically, post-hepatic jaundice occurs because of gallstones, pancreatitis and cancer of the pancreas. Pale stools, and dark urine is indicative of a post-hepatic cause of hyperbilirubinemia.

Neonatal Jaundice

• Hyperbilirubinemia in newborns is classified as physiologic or non-physiologic. Physiologic jaundice occurs in 50 to 60 percent of all newborns in the first few days of life, as reported by the University of California San Francisco Children's Hospital. This type of jaundice is non-pathological and generally lasts no more than a couple of weeks and does not cause problems for the infant, but there is a slight risk of bilirubin encephalopathy.

  Jaundice appearing within 24 hours, lasting longer than a week and accompanied by rising bilirubin levels indicates a pathological condition such as infection, Rh incompatibility, prematurity or congenital conditions such as herpes, syphilis or cytomegalovirus (CMV).

Gilbert's Syndrome

• An inherited genetic condition, Gilbert's syndrome causes inadequate processing of bilirubin. Generally there are no symptoms, but some do experience them. Symptoms common to Gilbert's syndrome include skin yellowing, fatigue, abdominal pain and general weakness. Diagnosis involves a blood test for bilirubin, complete blood count and liver studies.