Neonatal Jaundice

Etiology

The underlying etiology of neonatal jaundice is neonatal hyperbilirubinemia, which has 2 distinct types: unconjugated and conjugated hyperbilirubinemia, also known as indirect and direct hyperbilirubinemia, respectively. (See Image. Metabolic Pathway for Bilirubin in the Hepatocyte). 

Unconjugated Hyperbilirubinemia

Unconjugated (ie, indirect) hyperbilirubinemia (UHB) is the more common type and is either physiologic or pathologic. Physiologic jaundice accounts for 75% of neonatal hyperbilirubinemia and results from a physiologic alteration in neonatal bilirubin metabolism. Healthy adults have a total serum bilirubin (TSB) level of less than 1mg/dL. In neonates, normal TSB levels are comparatively higher, with age-dependant levels. Even healthy full-term newborns have an increased bilirubin load due to higher red blood cell (RBC) mass and decreased RBC lifespan. Metabolic bilirubin clearance is also compromised due to impaired activity of uridine diphosphate glucuronosyltransferase (UGT), the enzyme needed for bilirubin conjugation. The activity level of the newborn UGT enzyme is approximately 1% that of an adult.[7] Moreover, neonates also have increased enterohepatic circulation, further contributing to elevated TSB levels. Physiologic jaundice typically appears in full-term infants 24 hours after birth, peaks at around 48 to 96 hours, and resolves by 2 to 3 weeks.[2] Conversely, pathologic unconjugated hyperbilirubinemia occurs within the first 24 hours after birth when the TSB level is >95% on age-specific bilirubin nomograms or increases ≥5 mg/dL/day or >0.2 mg/dL/hour.[8] Based on the mechanism of bilirubin elevation, the etiology of unconjugated hyperbilirubinemia can be subdivided into the following 3 categories: increased bilirubin production, decreased bilirubin clearance, and miscellaneous.

Increased Bilirubin Production

The production of bilirubin can increase secondary to immune-mediated hemolysis caused by blood group incompatibilities (eg, such as ABO and Rhesus (Rh) incompatibility) and nonimmune mediated hemolysis, which is caused by RBC membrane defects (eg, hereditary spherocytosis and elliptocytosis), RBC enzyme defects (eg, glucose-6-phosphate dehydrogenase [G6PD], pyruvate kinase deficiencies), sequestration-like cephalohematoma, subgaleal hemorrhage, intracranial hemorrhage, polycythemia, and sepsis. Exaggerated immune or nonimmune mediated hemolysis is the most common cause of pathologic hyperbilirubinemia. Immune-mediated hemolysis occurs with blood group incompatibility as ABO/Rh incompatibility and causes hemolytic disease of the newborn (HDN). In HDN from ABO incompatibility, preformed maternal anti-A and anti-B antibodies of the immunoglobulin G (IgG) subclass cross the placenta and cause hemolysis and UHB in newborns with blood types A, B, or AB. Although the direct antiglobulin test (DAT) aids diagnosis, the sensitivity and positive predictive value for severe UHB are low.[9] ABO incompatibility between mother and fetus exists in about 15% of pregnancies, but HDN occurs in only about 4% of newborns with ABO incompatibility.[10] 

In Rh incompatibility, an Rh-negative mother, exposed to Rh-positive RBCs during a previous pregnancy, becomes sensitized and develops antibodies against Rh antigen. Initially, sensitization produces IgM antibodies that cannot cross the placenta. However, during subsequent pregnancies, IgG antibodies cross the placenta, causing RBC hemolysis in a fetus with Rh-positive blood. The Rh antigen is very immunogenic, and the resultant HDN is usually severe, often leading to hydrops fetalis or severe UHB in newborns. Prevention of neonatal UHB caused by immune-mediated hemolysis begins in pregnancy with the recognition of mothers at risk for developing Rh antibodies. The American College of Obstetricians and Gynecologists (ACOG) recommends that all Rh-negative pregnant women receive anti-D immune globulin at 28 weeks gestation and again after delivery if the infant is Rh-positive or the blood type is unknown.[11]

Nonimmune causes of UHB include RBC enzyme defects, RBC membrane defects, hemoglobinopathies, sepsis, sequestration, and polycythemia. Glucose-6 phosphatase dehydrogenase (G6PD) deficiency is the most common RBC enzyme defect, transmitted as an X-linked recessive trait. G6PD protects RBCs against oxidative damage by generating NADPH (nicotinamide adenine dinucleotide phosphate hydrogenase) from NADP (nicotinamide adenine dinucleotide phosphate). When exposed to oxidant stressors like illness, certain medications, dyes, and foods such as fava beans, G6PD deficient RBCs are hemolyzed, causing anemia and hyperbilirubinemia. More than 200 different mutations cause G6PD deficiency.[12] The clinical presentation differs depending on the variant, and some newborns may develop severe hyperbilirubinemia and bilirubin encephalopathy. Pyruvate kinase deficiency (PKD) is another condition that causes hemolysis and may present as UHB in newborns. PKD is an autosomal recessive (AR) disorder interfering with glycolysis and cellular energy production. In PKD, RBCs have shortened life spans, resulting in hemolytic anemia and UHB.[13]

Conditions causing UHB due to RBC membrane defects include hereditary spherocytosis (HS) and hereditary elliptocytosis (HE). HS (ie, Minkowski Chauffard disease) is the most common RBC membrane defect caused by RBC membrane protein mutations.[14] Most cases are transmitted as an autosomal dominant (AD) trait and can present in the neonatal period with UHB.[15] Hereditary elliptocytosis is another type of RBC membrane defect caused by structural membrane protein mutations in which elliptical-shaped RBCs are trapped in the spleen, leading to extravascular hemolysis and elevated TSB. HE is usually asymptomatic but may cause UHB in the neonatal period.[16] 

Etiologies that cause RBC sequestration (eg, cephalohematoma, subgaleal hemorrhage, and intracranial hemorrhage) are also risk factors for neonatal UHB due to increased bilirubin load. Polycythemia is another condition associated with an increased risk of UHB in newborns, associated with intrauterine growth restriction (IUGR), infants of diabetic mothers (IDM), large for gestational age (LGA) infants, maternal smoking, high altitude, twin to twin transfusions, and placental transfusion (eg, delayed cord clamping and umbilical cord milking). Studies show that delayed cord clamping reduces the incidence of postnatal anemia and leads to improved neurodevelopmental outcomes among term and preterm infants.[17][18] Delayed cord clamping has gained popularity but may also increase the risk of hyperbilirubinemia.[19][20]

Decreased Bilirubin Clearance

Indirect hyperbilirubinemia due to decreased bilirubin clearance usually results from quantitative or qualitative defects in the uridine diphosphate glucuronosyltransferase (UGT) enzyme. Gilbert syndrome and Crigler–Najjar syndrome type I and II are 3 disorders resulting from an abnormality of the UGT enzyme. Gilbert syndrome is the most common due to a mutation in the UGT1A1 gene leading to decreased UGT production and subsequent unconjugated hyperbilirubinemia.[21] Gilbert syndrome typically presents as mild jaundice at times of physiologic stress in the absence of hemolysis or liver dysfunction. However, presentations during the neonatal period are rare and usually associated with G6PD deficiency.[22][3] Crigler-Najjar syndrome type I is an AR disorder resulting from a complete absence of UGT activity. Affected patients present with severe hyperbilirubinemia in the first few days of life, often leading to bilirubin encephalopathy. Patients with Crigler-Najjar syndrome type II retain some of the activity of UGT enzymes; therefore, their TSB levels are not as elevated as in patients with the type I variant, and bilirubin encephalopathy rarely develops.[23]

Miscellaneous Causes

Other etiologies of UHG include congenital hypothyroidism, sulfa medications, ceftriaxone, penicillins, intestinal obstruction, pyloric stenosis, breast milk jaundice, and suboptimal intake with breastfeeding. Infants of mothers with diabetes are at higher risk of developing unconjugated hyperbilirubinemia. Jaundice secondary to breastfeeding and breast milk are 2 other common etiologies of UHB in newborns. Breastfeeding jaundice, known as suboptimal intake hyperbilirubinemia, occurs in the first week of life due to inadequate breast milk consumption, leading to dehydration and occasionally hypernatremia.[7] Poor intake decreases intestinal motility and elimination of bilirubin in the stool. Conversely, breast milk jaundice occurs late in the first week after birth, peaks in the second week, and usually resolves by 2 weeks of age, though the condition may persist for up to 3 months. Breast milk jaundice is rarely pathologic and is associated with adequate intake and good weight gain.[24] Inhibition of the UGT enzyme by pregnanediol and the deconjugation of conjugated bilirubin in the intestines by beta-glucuronidase present in breast milk is thought to be the primary underlying pathophysiology.[25][26]

Other miscellaneous causes of UHB include infants of mothers with diabetes (IDM), gastrointestinal obstruction, congenital hypothyroidism, and certain medications. IDM often have polycythemia, with an increased incidence of jaundice.[27] UHB in congenital hypothyroidism is related to decreased bilirubin hepatic uptake, impaired UGT activity, and sluggish gut motility, while gastrointestinal obstruction promotes increased bilirubin recycling by augmenting enterohepatic circulation. When prescribed in the neonatal period, certain medications may worsen UHB by displacing bilirubin from albumin, affecting albumin binding.[28] Sepsis can also predispose a newborn to UHB by causing oxidative damage to RBCs and increasing bilirubin load.[29]

Additionally, most infants with clinical UHB have a combination of 2 or more predisposing contributing factors, including prematurity, a history of jaundice requiring phototherapy in parents or siblings, Asian ethnicity, male gender, and exclusive breastfeeding.[2] Preterm infants are at increased risk of bilirubin encephalopathy and kernicterus and require close monitoring, although there is insufficient data and a lack of consensus guidelines on managing UHB in preterm infants.[30][31] Because of the increased risk of neurotoxicity, the TSB threshold for initiation of phototherapy is lower than for term infants. However, bilirubin is an antioxidant and may have a physiologic role in neonates.[32][33] Keeping TSB levels low by aggressive treatment in preterm infants may reduce this antioxidant level and potentially worsen retinopathy of prematurity. Moreover, reduced antioxidant status is also associated with chronic lung disease and neurological injury. Therefore, treating UHB in premature neonates is challenging without evidence-based guidelines. The most recent clinical practice guidelines for managing hyperbilirubinemia of the American Academy of Pediatrics in 2022 included only infants >35 weeks of gestation.[34][30]

Conjugated Hyperbilirubinemia

Conjugated hyperbilirubinemia (CHB), also referred to as neonatal cholestasis, is characterized by the elevation of serum conjugated (ie, direct) bilirubin (>1.0 mg/dL) due to impaired hepatobiliary function. Distinguishing CHB from UHB is critical because cholestatic neonatal jaundice is almost always pathologic and warrants prompt evaluation and treatment.[35] The causes of CHB are extensive and typically classified into the following categories:

• Infection: Congenital infections (eg, syphilis, toxoplasmosis, HIV, herpes virus, and rubella) should be included in the differential diagnosis of neonatal cholestasis, especially when stigmata of congenital infection, including growth restriction, coagulopathy, skin rash, or thrombocytopenia, are present. Cytomegalovirus (CMV) is also a common congenital infection with many manifestations. Most infected newborns are asymptomatic, but hepatomegaly and CHB may indicate hepatic involvement.[36] Carefully reviewing maternal history, specific serologies, and viral culture results aid diagnosis. Urine and blood cultures are also a component of the diagnostic evaluation, as urinary tract infections and septicemia can cause CHB in neonates. Additionally, microcirculatory changes in the liver, a direct effect of bacterial products, and toxins released by bacteria are thought to be the possible mechanisms of cholestasis in patients with UTI.[37]

• Obstruction of biliary flow: Conditions with this underlying pathophysiology include biliary atresia, choledochal cysts, neonatal sclerosing cholangitis, and neonatal cholelithiasis. Biliary atresia (BA) is the most common cause of conjugated hyperbilirubinemia in infants, with an incidence that varies by geographic location.[38] Taiwan, the region with the highest incidence, has a reported frequency of 1 in 6000 live births. In the United States, the incidence is about 1 in 12,000 live births.[39] The etiology of BA is not well understood, but genetic factors, viral infections, toxins, chronic inflammation, and autoimmune injury to bile ducts seem to play a role in the pathogenesis. The disease involves both intra-hepatic and extrahepatic bile ducts and classically presents around 2 to 4 weeks after birth with pale stools and jaundice. The initial ultrasound examination may reveal an absent gallbladder and the classic "triangular cord" sign, a ductal remnant of the extrahepatic bile duct.[40] Early diagnosis is critical to maximizing the response to the Kasai operation (ie, hepatic portoenterostomy).[41] If surgery is delayed until after 90 days of life, <25% of patients are likely to respond, compared to surgery performed within 60 days when >70% of patients will establish adequate bile flow.[42]

  Choledochal cysts can also cause biliary flow obstruction. The intrahepatic and extrahepatic bile ducts are dilated when choledochal cysts are present, and ultrasonography can detect cysts with normal or dilated intrahepatic bile ducts as opposed to the sclerosed ducts of biliary atresia. However, cystic biliary atresia may resemble choledochal cysts.[43] Neonatal sclerosing cholangitis (NSC) is a rare form of cholangiopathy that presents in infancy with CHB, hepatosplenomegaly, pale stools, and high serum gamma-glutamyltransferase activity (GGT).[44] Neonatal cholelithiasis is another rare entity that causes significant direct hyperbilirubinemia.[45]

• Genetic: There are several genetic etiologies (eg, Alagille syndrome, alpha-1 anti-trypsin deficiency, galactosemia, fructosemia, Tyrosinemia type 1, cystic fibrosis, progressive familial intrahepatic cholestasis [PFIC], Aagenaes syndrome, Dubin-Johnson syndrome, bile acid synthesis disorders [BSAD]) that commonly result in CHB. Alagille syndrome (ALGS) is an AD disorder caused by mutations in the JAG1 or NOTCH2 genes, leading to a lack of interlobular bile ducts.[46] With an incidence of 1 in 30,000 live births, ALGS is the most common cause of familial intrahepatic cholestasis, though CHB in patients with ALGS may resolve with age.[47][35] Characteristic clinical features include butterfly vertebrae, congenital heart defects (eg, peripheral pulmonic stenosis), kidney involvement, dysmorphic features (eg, broad forehead and a small pointed chin), and posterior embryotoxon of the eye. Gamma-glutamyl transferase (GGT) levels are elevated, often up to 20 times the standard value. Occasionally, patients with cystic fibrosis (CF) present with cholestasis because of abnormal bile that plugs the bile ducts.[48] In developing nations where newborn screening with immunoreactive trypsinogen is unavailable, neonatal cholestasis may be the first clue to diagnosing CF. 

  Alpha-1-antitrypsin deficiency is the most common genetic cause of cholestasis and can mimic biliary atresia in early infancy. Accumulation of anti-trypsin polymers in the hepatocyte endoplasmic reticulum of a patient with the PIZZ genotype leads to apoptosis of hepatocytes, ultimately resulting in cholestasis and cirrhosis later in childhood.[49] As with ALGS, cholestasis may improve with age. Galactosemia, fructosemia, and tyrosinemia type 1 are a few of the inborn errors of metabolism known to cause cholestasis in neonates. Newborns with galactosemia can present with cholestatic jaundice, cataracts, hepatomegaly, failure to thrive, renal tubular acidosis, and Escherichia coli sepsis after ingesting galactose from milk.[50] Galactose-1-phosphate uridyl transferase (GALT) deficiency leads to the accumulation of toxic galactose metabolites in multiple organs. The presence of urine-reducing substances suggests galactosemia, but GALT activity in the liver or erythrocytes confirms the diagnosis. Neonatal cholestasis is a presenting feature in hereditary tyrosinemia type 1, another AR disorder caused by a deficiency of the enzyme fumarylacetoacetate hydroxylase. Other characteristics of this disorder include renal Fanconi syndrome, hepatomegaly, coagulation abnormality, and the risk of hepatocellular carcinoma in untreated older patients.[51]

  Progressive familial intrahepatic cholestasis (PFIC) is a heterogeneous group of 3 genetic disorders involving canalicular hepatobiliary transport that presents with cholestasis.[52] Types 1 and 2 usually manifest in the neonatal period, while type 3 presents later in infancy. Affected patients with PFIC frequently develop cirrhosis and end-stage liver disease during childhood. In diagnostic studies, the GGT level is within the normal range in types 1 and 2 and elevated in type 3 patients. PFIC type 1 is caused by a mutation in the ATP8B1 gene, which encodes the FIC1 protein, whereas PFIC type 2 is caused by a mutation in the ABCB11 gene, which encodes for the bile salt excretory protein (BSEP). PFIC type 3 is caused by a mutation in the ABCB4 gene, which encodes for the multi-drug resistant-3 protein (MDR3).[53] Aagenaes syndrome, also known as lymphedema cholestasis syndrome (LCS), is another idiopathic familial intrahepatic cholestasis syndrome characterized by neonatal cholestasis and lymphedema in the lower extremities. Aagenaes syndrome is transmitted as an autosomal recessive (AR) trait usually seen in individuals of Norwegian descent.[54] Dubin-Johnson syndrome (DJS) is a rare AR disorder caused by a mutation in the ABCC2 gene, which codes for a non-biliary ion transporter in the liver. A unique feature of DJS is a black-colored liver and the excretion of coproporphyrin 1 in urine.[55] Bile acid synthesis disorder (BASD) results from a deficiency of an enzyme involved in synthesizing bile acids from cholesterol. BASDs are an uncommon cause of cholestasis, but many are curable with medical therapy.

• Miscellaneous: Other conditions that may cause CHD include idiopathic neonatal hepatitis, parenteral nutrition-induced cholestasis, gestational alloimmune liver disease, neonatal hemochromatosis, and hypotension. Parenteral nutrition-associated cholestasis (PNAC) is a significant iatrogenic cause of cholestasis in preterm infants managed with parenteral nutrition (PN). PNAC is present in about 20% of neonates receiving PN for 2 weeks or longer.[56] Duration of PN use and intestinal failure are 2 independent risk factors for PNAC. Though the mechanism is not entirely clear, likely being multifactorial, abnormal bile salt metabolism due to prematurity and the harmful effects of PN components are thought to be the main culprits.[57] Other factors, including sepsis and necrotizing enterocolitis, can also potentiate liver injury.[58] Gestational alloimmune liver disease (GALD), which causes almost all cases of neonatal hemochromatosis, is a fulminant alloimmune disorder and results from intrahepatic and extrahepatic iron deposition, leading to liver failure.[59] In GALD, maternal IgG immunoglobulin against fetal hepatocytes crosses the placenta, causing complement-mediated damage to fetal hepatocytes. Characteristic features involve signs of liver failure, including hypoglycemia, coagulopathy, hypoalbuminemia, cholestatic jaundice, edema, and elevated liver enzymes. GALD has a risk of recurrence in subsequent pregnancies of approximately 90% and can result in fetal or neonatal death.[60] The term idiopathic neonatal hepatitis is used when the etiology of neonatal cholestasis cannot be ascertained after an extensive diagnostic evaluation. Newer diagnostic tools enable more precise diagnoses, with fewer cases of neonatal cholestasis now classified as "idiopathic."[42] 

Epidemiology

Unconjugated hyperbilirubinemia is frequently encountered in the neonatal period. About 80% of term and preterm newborns will present with clinical jaundice with a TSB >5 mg/dL.[2][61] However, only approximately 10% of neonates require phototherapy.[62] Physiologic jaundice is the most frequent cause of clinical jaundice after the first day of life, estimated to account for 50% of cases.[63] Approximately 15% of breastfed infants will develop physiologic UHB lasting >3 weeks.[64]

Only a minority of jaundiced newborns have pathologic hyperbilirubinemia. Severe hyperbilirubinemia, commonly defined as a TSB>25 mg/dL, occurs in approximately 1 out of 2500 live births. Among these, ABO incompatibility, followed by G6PD deficiency, is the most frequently identified cause.[65] Newborns with Southeast and East Asian ancestry have higher recorded TSB levels than Black or White infants.[66][67] Neonatal jaundice also appears more common in infants living at high altitudes and around the Mediterranean Sea, especially in Greece.[68][69] 

Acute bilirubin encephalopathy occurs at a rate of approximately 1 in 10,000 live births, and the incidence of chronic bilirubin encephalopathy is comparitively lower, estimated at 1 in 50,000 to 100,000 live births.[70] However, developing nations report higher rates of kernicterus, a permanent neurologic condition.[71]

Conjugated hyperbilirubinemia is much less common than UHB, with an incidence of around 1 in 2500 term infants.[72] The most frequently identified cause of cholestatic jaundice in the neonatal period is biliary atresia, accounting for an estimated 25% to 40% of all cases, followed by infections and PN-induced cholestasis.[35][73] Approximately 60% to 70% of patients with BA will require liver transplantation in childhood, remaining the most common indication for a pediatric liver transplant.[74]

Pathophysiology

Bilirubin is produced from the catabolism of heme, a breakdown product of hemoglobin, in the reticuloendothelial system (RES). First, heme is converted to biliverdin, releasing iron and carbon monoxide via the action of the enzyme heme oxygenase.[75] Biliverdin is then converted to bilirubin by the enzyme biliverdin reductase. This hydrophobic unconjugated bilirubin binds to albumen, is transported to the liver, and is conjugated with glucuronic acid in the smooth endoplasmic reticulum by the enzyme uridine diphosphate-glucuronosyltransferase (UGT). Conjugated bilirubin is water soluble and is excreted in bile, passed into the gastrointestinal (GI) tract, and eliminated in feces. Some conjugated bilirubin is deconjugated in the GI tract by beta-glucuronidase and reabsorbed through the enterohepatic circulation.[76]

Newborn infants have higher TSB levels than adults due to higher hemoglobin levels at birth, a shorter RBC life span, and limited conjugating ability of the neonatal liver.[77] Healthy, full-term newborns typically have peak serum bilirubin concentrations of 5 to 6 mg/dL compared to adult levels of <1 mg/dL. Pathologic jaundice in neonates is related to increased production of bilirubin in the RES, impaired hepatic uptake, deficient conjugation of bilirubin, and enhanced enterohepatic circulation of bilirubin.[75] 

In severe hyperbilirubinemia, unbound, unconjugated bilirubin crosses the blood-brain barrier and binds to the brainstem, hippocampus, cerebellum, globus pallidus, and subthalamic nuclei.[2] At the cellular level, bilirubin inhibits certain mitochondrial enzymes, interferes with DNA and protein synthesis, induces breaks in DNA strands, and hampers phosphorylation.[78] Bilirubin also impairs tyrosine uptake and alters the normal functioning of N-methyl-D-aspartate–receptor ion channels.[79][80] These mechanisms are implicated in the pathogenesis of bilirubin toxicity that clinically manifests as bilirubin-induced neurologic dysfunction (BIND) and bilirubin encephalopathy. The duration of exposure to bilirubin and the amount of bilirubin in the brain determines the severity of brain damage. However, the TSB level does not correlate well with bilirubin toxicity without hemolysis.[75] Preterm infants are more vulnerable to the toxic effects of free unconjugated bilirubin. This may be related to comparatively lower serum albumin levels, CNS immaturity, and comorbidities such as intraventricular hemorrhage, periventricular leukomalacia, sepsis, necrotizing enterocolitis, and bronchopulmonary dysplasia.[71]

Conjugated hyperbilirubinemia results from abnormalities in the uptake, metabolism, transport, and excretion of bile salts and bilirubin, which increases bile acid in the liver, promoting the proliferation of bile ducts and fibrosis.[81] Bile acid is also responsible for the inflammation and apoptosis of hepatocytes, culminating in hepatocellular injury and cirrhosis.[82] Deficient bile secretion in cholestasis results in malabsorption of fat and fat-soluble vitamins A, D, E, and K and may lead to inadequate nutrition and weight gain.[83]

Histopathology

Kernicterus is derived from the German word kern, meaning core, referring to the basal ganglia. Yellow staining of deeper brain nuclei is seen on autopsy specimens of infants with severe unconjugated hyperbilirubinemia. Histopathologic findings include nuclei that have undergone pyknosis, cytoplasm vacuolation, and fading of the Nissl substance in neurons.[84] 

A liver biopsy is usually necessary for a definitive diagnosis of cholestasis as it helps to differentiate biliary atresia from idiopathic neonatal hepatitis. Histopathologic features of BA include the expansion of the hepatic portal tracts with edema, fibrodysplasia, bile ductular proliferation, and the presence of bile plugs in the ductal lumen. Multinucleate giant cells and hemopoiesis are also findings noted on histopathologic examinations of cholestatic liver samples.[85] Although not diagnostic of any particular disorder, the prominence of hepatic erythropoiesis is seen more frequently in cholestasis of infectious etiology. Pathognomonic histologic findings of other cholestatic conditions include periodic acid-Schiff (PAS) positive granules noted with alpha-1 antitrypsin deficiency, a paucity of bile ducts associated with Alagille syndrome, and periductal necrosis and inflammation seen in sclerosing cholangitis.[86] Among familial causes of cholestasis, canalicular cholestasis with a marked absence of ductular proliferation and isolated periportal biliary metaplasia of hepatocytes is commonly seen in patients with PFIC type 1. Though the histopathology of PFIC type 2 is similar, the altered liver architecture and extensive lobular and portal fibrosis with inflammation occur more frequently.[53]

History and Physical

The evaluation of the neonate with jaundice begins with a detailed history, including pregnancy complications, family history, delivery, the onset of associated symptoms, feeding adequacy, and maternal serologies. Stool and urine color may provide a clue about the type of jaundice. Minor risk factors are serum bilirubin in the high-intermediate range, macrosomic infants of diabetic mothers, polycythemia, male gender, and maternal age older than 25.[8] The American Academy of Pediatrics (AAP) recommends universal visual screening of all newborns for jaundice every 12 hours from the time of birth until the infant is discharged home. Furthermore, clinicians should identify risk factors for severe hyperbilirubinemia.[8] Major risk factors in newborns >35 weeks gestation include:[8]

• A bilirubin level in the high-risk zone before hospital discharge
• Jaundice in the first 24 hours after birth
• Maternal-fetal blood group incompatibility
• Gestational age <36 weeks [87]
• History of phototherapy in an immediate family member
• A cephalhematoma or significant bruising after delivery
• Exclusive breastfeeding
• Asian descent

To assess for jaundice, newborns should ideally be examined in daylight. However, clinical assessment is unreliable, especially if a newborn has received phototherapy or has dark skin.[88] Therefore, clinically significant jaundice should always be confirmed with a TSB or transcutaneous bilirubin (TcB). A focused physical examination may identify the cause of pathologic jaundice. Signs include pallor, petechiae, cephalohematoma, extensive bruising, hepatosplenomegaly, weight loss, and dehydration. All infants with jaundice should be assessed for clinical features of bilirubin encephalopathy, including poor feeding, lethargy, altered sleep, abnormal tone, and seizures. However, up to 15% of neonates with kernicterus are clinically asymptomatic in the newborn period.[75] Infants with signs and symptoms suggesting neonatal cholestasis often have multisystem involvement, which may guide diagnostic investigations.

Evaluation

Diagnosis Studies in Unconjugated Hyperbilirubinemia

The AAP recommends an infant's bilirubin levels should be assessed between 24 and 48 hours after birth. If an infant leaves the hospital prior to this time frame, a bilirubin level should be measured before discharge home. Bilirubin levels are initially evaluated with a transcutaneous measurement device or blood samples for total serum bilirubin.[89] Transcutaneous estimation of bilirubin can be used as a screening test for hyperbilirubinemia to reduce the frequency of blood tests, but the utility is limited in infants with dark skin and following phototherapy use.[90][91] The serum level should be measured when the transcutaneous bilirubin (TcB) level exceeds the 95th percentile on the transcutaneous nomogram or 75% of the TSB threshold for phototherapy. Another limitation of the TcB is the inability to detect the direct fraction of bilirubin required for diagnosing neonatal cholestasis.

Recommended studies to identify a hemolytic disease etiology of unconjugated hyperbilirubinemia include maternal and neonatal blood types, a direct antibody test (DAT), complete blood cell (CBC), reticulocyte count, blood smear, and G6PD testing. Serum albumin, considered a surrogate marker for free bilirubin, should be checked, especially if the TSB level approaches the level where exchange transfusion is indicated. Free bilirubin is the fraction responsible for bilirubin-induced toxicity.[92] The bilirubin-albumin ratio (B/A) ratio is an additional tool that may predict the risk of kernicterus and serve as a guide when considering the escalation of care and exchange transfusion.

Radiographic imaging is usually not required for most cases of UCH. Brain magnetic resonance imaging (MRI) findings have high sensitivity for bilirubin encephalopathy, with posteromedial borders of the globus pallidus being the most sensitive region for detecting signal changes. Infants with bilirubin encephalopathy demonstrate hyperintense signals on T1-weighted sequences in the acute stage that eventually become hyperintense on T2-weighted sequences as the condition evolves. Magnetic resonance spectroscopy (MRS) shows increased levels of glutamate and decreased levels of N-acetyl-aspartate and choline.[93] However, the absence of these findings does not exclude the risk of chronic bilirubin encephalopathy.

Diagnostic Studies in Conjugated Hyperbilirubinemia

Serum aminotransferases may provide evidence of hepatocellular injury in patients with conjugated hyperbilirubinemia. Alkaline phosphatase and elevated GGT levels may indicate an obstruction in biliary channels. The prothrombin time (PT), the international normalized ratio (INR), and serum albumin evaluate hepatic synthesis and function. Additional tests like TORCH titers for in-utero infections, urine cultures, viral cultures, serologic titers, newborn screening, tests for inborn errors of metabolism, alpha-1 antitrypsin phenotype, and genetic profiles may be diagnostic.

Radiology may be necessary to evaluate neonatal cholestasis. Hepatic ultrasonography can identify sludging in the biliary tree, gallstones, inspissated bile, and choledochal cysts. A triangular cord sign on hepatic ultrasound has high sensitivity and almost 100% specificity for biliary atresia.[81] Hepatobiliary scintigraphy is another modality utilized to evaluate neonatal cholestasis. Decreased excretion of the tracer 24 hours after introduction suggests obstruction and further differentiates obstructive and nonobstructive causes of cholestasis.[94] Prior treatment with phenobarbital improves the sensitivity of hepatobiliary scintigraphy. However, a liver biopsy is the gold standard for diagnosing neonatal cholestasis. Histopathologic interpretation by an experienced pathologist will identify the correct diagnosis in 90% to 95% of cases and may prevent unnecessary interventions in patients with intrahepatic cholestasis.[95]

Treatment / Management

Treatment of Unconjugated Hyperbilirubinemia

Phototherapy and exchange transfusion are the mainstays of treatment for newborns with unconjugated hyperbilirubinemia. Other treatment modalities may be utilized based on patient response to these therapies. The approach to treatment is determined by the neurotoxicity risk factors present, neonatal gestational age, and hour-specific TSB.[8](A1)

Phototherapy

Phototherapy (PT) remains the first-line treatment for managing pathologic unconjugated hyperbilirubinemia. PT reduces TSB to safe levels and decreases the risk of bilirubin toxicity and the need for exchange transfusion. The TSB level at which PT is indicated is determined based on the risk factors for neurotoxicity present, the infant's gestational age, and hour-specific TSB.[34][8] Risk factors for neurotoxicity that lower the TSB threshold to initiate PT include:[34][8] (A1)

• Neonatal gestational age <38 weeks
• Serum albumin <3.0 g/dL
• Positive DAT or diagnosis of G6PD deficiency or other hemolytic diseases
• Sepsis
• Significant clinical deterioration in the preceding 24 hours

However, for premature infants, few standardized guidelines exist, and most hospitals compile their own protocols for phototherapy and exchange transfusion in preterm infants based on birth weight and gestational age.[31] The efficacy of phototherapy depends on the dose and wavelength of light used, as well as the infant's exposed surface area. Increasing the dose of PT can be achieved by placing phototherapy units at a minimum safe distance from the infant and increasing the number of units used.

Bilirubin optimally absorbs light in the blue-green range (ie, 460-490 nm). The underlying mechanism of PT involves inducing photoisomerization and converting bilirubin into lumirubin, which is readily excreted into bile and urine.[96] During phototherapy, the neonate's maximum body surface area should be exposed to the light source while keeping the eyes covered to avoid retinal injury, and interruptions should be minimized. The maintenance of hydration is necessary to ensure adequate urine output, as most bilirubin is excreted in the urine as lumirubin, a structural isomer of bilirubin formed during phototherapy. Therefore, breastfeeding support should be offered to all nursing mothers as early initiation of breastfeeding and frequent, on-demand feeding decreases the likelihood of dehydration. Although supplemental oral water and dextrose water are not recommended, supplemental pumped breastmilk or infant formula can be considered for feeding issues, including infants with ineffective sucking or latching or inadequate maternal milk production.[34] 

After phototherapy is discontinued, there may be an increase in the total serum bilirubin level, known as the rebound bilirubin. This level is usually lower than the pretreatment level and rarely requires reinitiation of phototherapy.[97] PT is considered safe, but recent evidence suggests a possible association with long-term sequelae, including a small risk of epilepsy. However, no studies have proven causation.[98] A few studies also have reported a possible association between solid organ tumors and nonlymphocytic leukemias and children treated with phototherapy.[99][100] Adverse effects of PT include rashes, dehydration, hypocalcemia, retinal damage, hemolysis due to oxidative damage, delay in patent ductus arteriosis closure in preterm infants, and allergic reactions.[101] Bronze baby syndrome is a self-limited condition associated with elevated levels of conjugated bilirubin that rarely occurs with PT, resulting in irregular, bronze-gray pigmentation of the skin, mucous membranes, and urine. The phenomenon's mechanism is unclear but appears to be related to the accumulation of bilirubin and biliverdin photoisomers. Bronze baby syndrome usually resolves within a few days of discontinuing phototherapy; however, the prognosis depends upon the underlying cause of the conjugated hyperbilirubinemia.[102][103](B2)

Exchange Transfusion

In 1947, exchange transfusion (ET) was the first successful treatment for jaundice.[104] Now, ET is the second-line treatment for severe unconjugated hyperbilirubinemia since phototherapy was developed in the 1950s.[105][106] Indications for this therapy include neonatal failure to respond to PT or a TSB level at the exchange transfusion threshold. The threshold to initiate exchange transfusion is calculated based on several factors, including the TSB level and rate of rise, neonatal age (ie, hours or days since birth), and risk factors for neurologic complications.[34] ET rapidly removes bilirubin and hemolysis-causing antibodies from the infant's circulation. A double-volume exchange blood transfusion (160-180 ml/kg) is performed, replacing aliquots of the neonate's blood with crossed-matched donor blood. Since most of the total body bilirubin is extravascular, the TSB level immediately following ET is approximately 60% of the pre-exchange level, but that later increases to 70% to 80% of the pretreatment level as a result of equilibrium. During ET, the neonate's vital signs should be monitored closely. Following the procedure, TSB, CBC, serum calcium, glucose, and electrolytes should be rechecked due to potential complications, including electrolyte abnormalities (eg, hypocalcemia and hyperkalemia), cardiac arrhythmias, thrombocytopenia, blood-borne infections, portal vein thrombosis, graft versus host disease, and necrotizing enterocolitis (NEC).[107][108] Phototherapy should resume after exchange transfusion until the bilirubin reaches a level where PT can be safely discontinued. (B2)

Intravenous Immunoglobulin

Intravenous immunoglobulin (IVIG) is used when immune-mediated hemolysis is the cause of unconjugated hyperbilirubinemia, which prevents RBC hemolysis by coating Fc receptors on RBCs.The AAP recommends IVIG infusion in immune-mediated hemolysis if TSB remains within 2 to 3 mg/dL of the exchange threshold despite intensive phototherapy.[109][110] However, the evidence that IVIG reduces the need for ET is unclear. Nonetheless, IVIG is often used in clinical practice to manage severe unconjugated hyperbilirubinemia.(A1)

Treatment of Conjugated Hyperbilirubinemia

Treatment of conjugated hyperbilirubinemia is tailored to the specific etiology of the jaundice. To achieve the best outcomes, patients diagnosed with biliary atresia require a Kasai operation (hepatic portoenterostomy) within the first 2 months of life to prevent irreversible liver damage.[41] The surgery involves the removal of the atretic biliary ducts and fibrous plate and anastomosis of the jejunum with the remaining ducts by a Roux-en-Y procedure to provide an alternative pathway for biliary drainage.[111] Infectious causes of cholestasis are treated with specific antimicrobial agents, whereas treatment with cholic acid and chenodeoxycholic acid is often curative for many BASDs. Patients with GALD appear to respond well to IVIG and double-volume exchange transfusion. Patients with conditions of cholestasis (eg, GALD and biliary atresia) and severe hepatic damage may require liver transplantation, which is curative but technically challenging in infants.[60] Parenteral nutrition-induced cholestasis is managed with cyclic PN, reducing the duration of exposure and initiating enteral feeds as early as possible. The manganese and copper content of PN should be monitored closely to minimize liver injury.(B2)

Differential Diagnosis

The differential diagnoses of jaundice are extensive. (Refer to the Etiologies section for more information on the causes of jaundice). The onset of neonatal jaundice should prompt a timely evaluation to determine if the underlying etiology is a self-limited physiologic condition or a disease requiring treatment. Any neonate with yellowish skin and sclerae should be clinically diagnosed with jaundice. High carotene levels may cause yellowish skin that mimics jaundice in older infants and children who are ingesting diets of breast milk or foods high in beta-carotene.[112][38] However, with carotenemia, the sclera or mucosa are not involved, and neonates are not born with this benign condition. Visual assessment of the degree of jaundice is an unreliable screening tool for clinically significant hyperbilirubinemia. All newborns should undergo an appropriate evaluation for possible jaundice before hospital discharge.[113][114] 

Staging

Acute Bilirubin Encephalopathy

The manifestations of bilirubin encephalopathy in neonates with severe unconjugated hyperbilirubinemia depend on when the symptoms appear. The level at which unconjugated bilirubin becomes neurotoxic is unclear, and kernicterus has been reported in infants without markedly elevated bilirubin levels on autopsy. There are 3 phases of acute bilirubin encephalopathy, including:

• Phase 1: The symptoms of phase 1 appear during the first 1 to 2 days of illness and are notable for poor feeding, lethargy, hypotonia, irritability, or frank seizures.
• Phase 2: If infants continue to deteriorate, they progress to phase 2, characterized by increased extensor muscle tone, exhibiting opisthotonus and retrocollis. This typically occurs during the middle of the first week of illness.
• Phase 3: After the first week, muscle rigidity, stupor or coma, apnea, or seizures may occur.

Chronic Blirubin Encephalopathy

This permanent and disabling neurologic condition, also known as kernicterus, is present in 2 forms, depending on the timing of symptoms.

• In the first year: These patients present with hypotonia, exaggerated deep tendon reflexes, obligatory tonic neck reflexes, and delayed motor milestones.
• Beyond the first year: Patients exhibit movement disorders, most commonly choreo-athetoid cerebral palsy, dental enamel hypoplasia, upward gaze abnormality, and sensorineural hearing loss.[75]

Prognosis

With treatment, the prognosis for most cases of unconjugated hyperbilirubinemia is excellent. In patients with delayed or inadequate treatment, bilirubin encephalopathy may ensue. The burden of bilirubin encephalopathy is significantly higher in developing and resource-limited nations.[71] Reports suggest a resurgence of kernicterus in countries where this complication had virtually disappeared, primarily attributed to the early hospital discharge of newborns with inadequate follow-up. Patients with Crigler-Najjar type I carry a poor prognosis and require liver transplantation for a definitive cure. In the absence of liver transplantation, bilirubin encephalopathy is common.

The prognosis for conjugated hyperbilirubinemia depends on the etiology. The prognosis of patients with biliary atresia is significantly improved by early diagnosis and surgery within 60 days of life. Similarly, patients with bile acid synthesis disorder (BASD) have excellent outcomes and respond well to medical treatment. Historically, the outlook for gestational alloimmune liver disease (GALD) was poor, with up to 80% mortality without liver transplantation. However, with the advent of IVIG use and double volume exchange transfusion, the prognosis has significantly improved in recent years.[115] The outlook for most other causes of cholestasis is often unfavorable, and many patients will require multidisciplinary interventions.

Complications

Newborns with severe hyperbilirubinemia are at risk for bilirubin-induced neurologic dysfunction (BIND). Bilirubin binds to the globus pallidus, hippocampus, cerebellum, and subthalamic nuclear bodies, causing neurotoxicity.[116] Acute bilirubin encephalopathy (ABE) is characterized by lethargy, hypotonia, and decreased sucking. At this stage, the condition is reversible. However, if ABE progresses, patients can develop irreversible chronic bilirubin encephalopathy or kernicterus. ABE manifests as choreo-athetoid cerebral palsy, seizures, arching, posturing, gaze abnormalities, dental enamel defects, and sensorineural hearing loss. Infants with neonatal cholestasis are also at risk of developing liver failure, cirrhosis, and even hepatocellular carcinoma in rare cases. Long-standing cholestasis may also lead to failure to thrive and fat-soluble vitamin deficiencies.