Hyperbilirubinemia

Elevated serum bilirubin levels and mild jaundice are hallmarks of hyperbilirubinemia, also known as neonatal jaundice. The disorder can be physiologic (with jaundice the only symptom) or pathologic (resulting from an underlying disease). Physiologic jaundice is widespread and is more common and severe in certain ethnic groups (Chinese, Japanese, Koreans, Native Americans) whose mean peak of unconjugated bilirubin is about twice that of the rest of the population.

Physiologic jaundice is self-limiting; the prognosis for pathologic jaundice varies, depending on the cause. Untreated, severe hyperbilirubinemia may cause kernicterus, a neurologic syndrome resulting from deposition of unconjugated bilirubin in the brain cells and characterized by severe neural symptoms.

Causes

Hyperbilirubinemia may develop when:

• factors that disrupt conjugation and usurp albuminbinding sites are present, including drugs such as aspirin, tranquilizers, and sulfonamides and conditions such as hypothermia, anoxia, hypoglycemia, and hypo­albuminemia
• decreased hepatic function results in reduced bilirubin conjugation
• increased erythrocyte production or breakdown results from hemolytic disorders or from Rh or ABO incompatibility
• biliary obstruction or hepatitis results in blockage of normal bile flow
• maternal enzymes present in breast milk inhibit the infant's glucuronyl-transferase conjugating activity.

Hyperbilirubinemia stems from hemolytic processes in the neonate. As erythrocytes break down at the end of the neonatal life cycle, the hemoglobin separates into globin (protein) and heme (iron) fragments. Heme fragments form unconjugated (indirect) bilirubin, which binds with albumin for transport to liver cells to conjugate with glucuronide, forming direct bilirubin. Because unconjugated bilirubin is fat-soluble and can't be excreted in urine or bile, it may escape ro extravascular tissue, especially fatty tissue and the brain, resulting in hyperbilirubinemia.

Symptoms

The following are the most common symptoms of hyperbilirubinemia. However, each baby may experience symptoms differently. Symptoms may include:

• yellow coloring of the baby's skin (usually beginning on the face and moving down the body)
• poor feeding or lethargy

The symptoms of hyperbilirubinemia may resemble other conditions or medical problems. Always consult your baby's physician for a diagnosis.

Diagnostic tests

Jaundice and elevated levels of serum bilirubin confirm hyperbilirubinemia.

Both mother and infant should be tested for blood group incompatibilities, and their hemoglobin levels and hematocrit should be measured. The direct Coombs' test also should be performed on both mother and infant. Diagnostic procedures for hyperbilirubinemia may include:

• direct and indirect bilirubin levels
• red blood cell counts
• blood type and testing for Rh incompatibility (Coomb's test)

Treatment

Depending on the underlying cause, treatment may include phototherapy, exchange transfusions, albumin infusion and, possibly, drug therapy. Phototherapy is the treatment of choice for physiologic jaundice and pathologic jaundice due to hemolytic disease of the newborn (after the initial exchange transfusion). Phototherapy uses fluorescent light to decompose bilirubin in the skin by oxidation. It usually is discontinued after bilirubin levels fall below 10 mg/dl and continue to decrease for 24 hours. Phototherapy seldom is the only treatment for jaundice due to a pathologic cause.

An exchange transfusion, replacing the infant's blood with fresh blood (less than 48 hours old), thus removing some of the unconjugated bilirubin in serum, may be performed for severe hyperbilirubinemia.

Other therapy for excessive bilirubin levels includes albumin administration (1 g/kg of 25% salt-poor albumin), which provides additional albumin for binding unconjugated bilirubin. This can be done 1 to 2 hours before exchange or as a substitute for a portion of the plasma in the transfused blood.

Drug therapy, which is rare, usually consists of phenobarbital administered to the mother before delivery and to the infant several days after delivery This, drug stimulates the hepatic glucuronide-conjugating system.

Prevention

While hyperbilirubinemia cannot be totally prevented, early recognition and treatment are important in preventing bilirubin levels from rising to dangerous levels.

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