Laboratory Studies
The following laboratory studies may be included in the workup:
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Serum bilirubin (total and direct): Conjugated hyperbilirubinemia, defined as any level exceeding either 1 mg/dL (total bilirubin < 5 mg/dL) or 20% of total bilirubin (total bilirubin >5 mg/dL), is always abnormal. Interestingly, infants with biliary atresia typically show only moderate elevations in total bilirubin, which is commonly 6-12 mg/dL, with the direct (conjugated) fraction comprising 50-60% of total serum bilirubin. [16]
- A study by Shneider et al found that infants whose total bilirubin does not fall below 2.0 mg/dL within 3 months of hepatoportoenterostomy were at high risk for early disease progression, suggesting they should be considered for liver transplantation in a timely fashion. The study also added that interventions increasing the likelihood of achieving total bilirubin < 2.0 mg/dL within 3 months of hepatoportoenterostomy may enhance early outcomes. [17]
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Alkaline phosphatase (AP), 5' nucleotidase, gamma-glutamyl transpeptidase (GGTP), serum aminotransferases, serum bile acids
These candidate tests have been proposed as a means to increase both sensitivity and specificity of routine laboratory evaluation. Unfortunately, no single biochemical determination accurately discriminates between biliary atresia and the other causes of neonatal cholestasis.
In addition to direct hyperbilirubinemia (a universal finding in neonatal cholestasis), enzyme abnormalities include elevated AP levels. In some cases, skeletal sources of AP can be differentiated from hepatic sources by measuring the liver-specific AP fraction, 5' nucleotidase.
GGTP is an integral membrane protein of the bile canaliculus and is elevated in cholestatic conditions. GGTP levels closely correlate with AP findings and are increased in all biliary obstructive conditions. However, GGTP levels may be within the reference range in some forms of cholestasis of hepatocellular origin.
Aminotransferase levels are not particularly helpful in establishing a diagnosis, although a markedly elevated alanine aminotransferase level (>800 IU/L) indicates significant hepatocellular injury and is more consistent with the neonatal hepatitis syndromes.
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Serum alpha1-antitrypsin with Pi typing: Alpha1-antitrypsin deficiency is the most common inherited liver disease that presents with neonatal cholestasis. The abnormal PiZZ phenotype, as determined by electrophoresis, is associated with neonatal cholestasis in approximately 10% of subjects.
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Sweat chloride (Cl): Biliary tract involvement is a well-recognized complication of cystic fibrosis (CF), and an association between meconium ileus in the newborn and cholestasis has been described. A diagnosis of CF should be strongly considered in any infant with direct hyperbilirubinemia, particularly if other associated signs or symptoms (ie, respiratory, GI) are present. Sweat Cl iontophoresis remains the criterion standard for diagnosing CF.
Imaging Studies
Ultrasonography
In neonatal cholestasis syndromes, ultrasonography can exclude specific anomalies of the extrahepatic biliary system, particularly choledochal cysts. Today, a diagnosis of choledochal cyst should be made in utero using fetal ultrasonography.
In biliary atresia, ultrasonography may demonstrate absence of the gallbladder and no dilatation of the biliary tree. [18] Unfortunately, the sensitivity and specificity of these findings, even in the most experienced centers, probably do not exceed 80%. For this reason, ultrasonography has been found unreliable in the evaluation of biliary atresia.
Hepatobiliary scintiscanning
Hepatobiliary imaging, using technetium-labeled diisopropyl iminodiacetic acid (DISIDA) nuclear scintiscan, is useful in evaluating infants with suspected biliary atresia. Unequivocal evidence of intestinal excretion of radiolabel confirms patency of the extrahepatic biliary system.
Two cautionary notes are required. First, reliability of the scintiscan is diminished at very high conjugated bilirubin levels (>20 mg/dL). Second, the test has been associated with a 10% rate of false-positive or false-negative diagnostic errors.
Other Tests
Duodenal intubation and duodenal string test
These studies are performed in some centers to evaluate duodenal bile excretion; however, in the author's experience, these studies are cumbersome, time-consuming, and unreliable.
Endoscopic retrograde cholangiopancreatography (ERCP)
This diagnostic procedure has previously been unavailable for use during infancy because of technical considerations. However, endoscope manufacturers are now producing side-viewing instruments that may be successfully used in neonates.
Although not yet widely used, reports have demonstrated the use of ERCP in diagnosing biliary atresia; one recent study reported a diagnosis of biliary atresia in 5 infants undergoing ERCP for neonatal cholestasis. With continued refinement and wider use of this diagnostic modality, ERCP may become part of the management algorithm in assessing neonatal direct hyperbilirubinemia, for which other studies have failed to confirm a diagnosis. [19]
Procedures
Percutaneous liver biopsy
Percutaneous liver biopsy is widely regarded as the most valuable study for evaluating neonatal cholestasis. Morbidity is low in patients without coagulopathy. When examined by an experienced pathologist, an adequate biopsy specimen can differentiate between obstructive and hepatocellular causes of cholestasis, with 90% sensitivity and specificity for biliary atresia. See the image below.
Bile ductular proliferation in liver biopsy specimen (hematoxylin and eosin stain) from patient with biliary atresia. Also note hepatocellular bile staining as a consequence of cholestasis.
Several cholestatic conditions, including biliary atresia, may demonstrate an evolving histopathological pattern. Accordingly, biopsies are not usually diagnostic in those younger than 2 weeks, and serial samples, usually at 2-week intervals, may be required to reach a definitive diagnosis.
Intraoperative cholangiography
This procedure definitively demonstrates anatomy and patency of the extrahepatic biliary tract. Perform intraoperative cholangiography when liver biopsy findings suggest an obstructive etiology. The study is also indicated when biopsy results are equivocal or scintiscan fails to demonstrate clear evidence of duodenal bile excretion.
Histologic Findings
Despite the fact that several variants of extrahepatic biliary atresia have been described, suggesting a role for both ontogenic and acquired causes, no discernible qualitative differences in histopathological characteristics are evident. Surgical specimens demonstrate a spectrum of abnormalities, including active inflammation with bile duct degeneration, a chronic inflammatory reaction with proliferation of both ductular and glandular elements, and fibrosis. The progressive nature of the disorder is confirmed by its evolving histological picture.
Ultimately, evidence of biliary tract obstructive disease confirmed by liver biopsy findings determines which infants require exploratory laparotomy and intraoperative cholangiography. Portal bile ductular proliferation, bile plugging, portal-portal fibrosis, and an acute inflammatory reaction are characteristic findings in infants with neonatal cholestasis of an obstructive etiology.
Periodic acid-Schiff (PAS) staining of biopsy tissue can also be used to confirm a diagnosis of alpha1-antitrypsin deficiency by finding intracellular PAS-positive granules resistant to digestion by diastase.
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Biliary atresia.
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Bile ductular proliferation in liver biopsy specimen (hematoxylin and eosin stain) from patient with biliary atresia. Also note hepatocellular bile staining as a consequence of cholestasis.
