Hyperbilirubinemia: Recognition, Care and Management of Term and Near-Term Infants

Objectives

What is the Problem?

Definition of Terms

Production, Metabolism, Transport and Excretion

Assessment

Practice Standard

Current Treatment

Education

Bibliography

Quiz

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What are the Causes of Increased Bilirubin Production?

The breakdown of a red blood cell (RBC) releases hemoglobin and produces bilirubin. The rate of bilirubin production in the newborn is two to three times that of an adult. Causes of increased bilirubin production include the following:

• Neonates have more RBC's per kilogram of body weight than adults.
• The RBC lifespan is shorter (70-90 days) than that of an adult (120 days).
• Enterohepatic shunting often is increased in the neonate.
• Heme is an essential molecule in all oxygen dependent metabolism and every cell is a potential source of bilirubin. These non-RBC sources of heme are also increased in the neonate.

What is the Process of Bilirubin Conjugation?

Once produced, bilirubin must be transported, conjugated and ultimately excreted from the body. Bilirubin metabolism begins in the reticuloendothelial system, primarily in the liver and spleen, with the removal of old or abnormal erythrocytes from circulation. The hemoglobin molecule is metabolized into heme, globin and iron. Heme is converted to bilirubin, which is transformed rapidly into the unconjugated form of bilirubin and then released into plasma.

Unconjugated bilirubin is bound to albumin in the plasma. If all the sites on the albumin are taken or the bilirubin has a decreased affinity for albumin, the unconjugated bilirubin is unbound (free) in the plasma. Unbound bilirubin has an increased potential for movement into the tissues, such as the skin or across the blood-brain barrier.

Bilirubin conjugation is essential for excretion of bilirubin. It occurs in the smooth endoplasmic reticulum of the liver. Conjugation involves combining indirect bilirubin with glucose and glucuronic acid to produce a water-soluble substance known as direct bilirubin. Eighty percent of bilirubin is conjugated and excreted into the bile and intestine. This process requires oxygen and glucose, and may be affected adversely in those newborns who have difficulty maintaining oxygen and glucose levels. Conjugated bilirubin is excreted:

• Into the intestine in the stool as stercobilin.
• A small amount by the kidneys as urobilinogen.

Delayed stooling potentially increases reabsorption of bilirubin from the bowel.