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Jaundice is defined by a serum bilirubin concentration greater than 5 mg/dL. Clinical jaundice develops in 50% of newborns, and breast-feed infants have an increased incidence of jaundice. Differentiation between physiologic jaundice, which is seen in many infants during the first week of life, and pathologic jaundice is essential because pathologic jaundice is a sign of a more serious condition.
I. Pathophysiology A. Physiologic versus pathologic jaundice

1. Physiologic jaundice is characterized by unconjugated hyperbilirubinemia thatpeaks by the third or fourth day of life in full-term newborns and then steadily declines by 1 week of age. Asian newborns tend to have higher peak bilirubin concentrations and more prolonged jaundice. Premature infants are more likely to develop jaundice than full-term babies.


2. Causes of physiologic jaundice

a. Increased bilirubin load due to the high red blood cell volume in newborns and shortened blood cell survival.

b. Deficient hepatic uptake and deficient conjugation of bilirubin.

c. Increased enterohepaticbilirubinreabsorption.

d. Deficient excretion of bilirubin.

3. Pathologic jaundice usually appears within the first 24 hours after birth and is characterized by a rapidly rising serum bilirubin concentration (>5 mg/dL per day),prolonged jaundice (>7 to 10 days in a full-term infant), or an elevated directbilirubinconcentration(>2mg/dL).Conjugated hyperbilirubinemia never has a physiologic cause and must always be investigated.

II. Clinical evaluation of jaundice in newborns
A. History may reveal abdominal distention, delayed passage of meconium,lethargy, light colored stools, dark urine, lowApgar scores, poor feeding, weight loss, or vomiting.

B. Physical examination should seek bruising, cephalhematoma,congenitalanomalies,hepatosplenomegaly, pallor, petechiae, or small or large size for gestational age.
C. Maternalhistoryshould assess historyofchorioamnionitis, forceps delivery, vacuum extraction, diabetes, dystocia, or exposure to drugs. Failure to receive immune globulin in a previous pregnancy or abortion that involved risk of isoimmunization should be sought. Family history of jaundice, anemia, liver disease, splenectomy, Greek or Asian race, preeclampsia, or unexplained illness during pregnancy should be assessed.

III. Laboratory evaluation
A. Diagnostic tests include blood group typing of both mother and infant, a direct Coombs' test, and measurementofserum bilirubin concentration.

B. Ill or premature infants, or those with significant jaundice (serum bilirubin >15 mg/dL) require a complete blood cell countorhemoglobin, reticulocyte count, blood smear, and direct bilirubin level. IninfantsofAsianorGreek descent,glucose-6-phosphate dehydrogenase (G6PD) should be measured.
IV. Differential diagnosisofunconjugatedhyperbilirubinemia A. Increased bilirubin production

1. Fetal-maternal blood group incompatibility is one cause of increased bilirubin production. Rh sensitization occurs when an Rh-negative mother is exposed to Rh-positive blood cells. Subsequent Rh-positive fetuses may develop hemolysis.Other minor blood group incompatibilities also can cause hemolysis and jaundice.
2. ABO incompatibility is the most common type of isoimmune hemolytic disease. It can occur when the mother's blood group is O and the baby’s is A or B. This type of hemolysis is relatively mild.

3. G6PD deficiency, a sex-linked disease, is an important cause of hyperbilirubinemia and anemia in infants of Greek and Asian descent.

4. Abnormalities of the red blood cell membrane, such as spherocytosis and elliptocytosis, may cause hyperbilirubinemia. Alpha thalassemia may occur in the neonatal period.

5. Hematoma, occult hemorrhage,orpolycythemia (fetomaternal or twin-to-twin transfusion, delayed cord clamping, intrauterine growth retardation, or maternal diabetes)maylead to hyperbilirubinemia.

B. Decreased bilirubin excretion
1. Delay in intestinal transit time, because bowel obstruction, increases the enterohepatic circulation. Relief of the obstruction results in a decline in bilirubin concentration.

2. Crigler-Najjar syndrome is a rare, inherited, lifelong deficiency of bilirubin excretion. Type I is autosomal recessive. Patients present with extreme jaundice(bilirubin concentration >25 mg/dL) and have a very high risk of bilirubin encephalopathy. Type II is autosomal dominant, and it can effectivelybe treated with phenobarbital.

3. Neonatal hypothyroidism is another cause of prolonged indirect hyperbilirubinemia.

C. Increased bilirubin production and decreased excretion.Sepsis often causes increased breakdown of red blood cells and decreased hepatic excretion of bilirubin. Certain drugs given to the newborn may also induce hemolysis or decrease bilirubin excretion.

D. Breast feeding is associated with neonatal hyperbilirubinemia. In healthy newborns, the danger of an elevated bilirubin concentration is minimal, and switching to formula feeding is unnecessary.
V. Consequences of unconjugated hyperbilirubinemia. Bilirubin encephalopathy (kernicterus) is defined as the acute and often fatal syndrome characterized by opisthotonos, hypotonia, a high-pitched cry, and late neurologic sequelae of choreoathetosis, spasticity, upward-gaze paresis, and central hearing loss.

VI. Treatment
A. Low-risk infants with minimal jaundice are observed for an increase in the jaundice intensity or a spread to the baby’s feet (jaundice advances from head-to-foot).
B. Phototherapywith blue lightcauses photoconversion of bilirubin to a water-soluble product that is excreted in urine and stool. Bilirubin concentrations are measured once or twice a dayduring phototherapy, and treatment is discontinued when the bilirubin concentration drops below 12 mg/dL.
C. Exchange transfusion therapy. Exchange transfusion is used for emergent treatment of markedlyelevated bilirubin and for correction of anemia caused byisoimmune hemolytic disease