Pediatric emergency medicine trisk 219
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It is important to note the difference between “direct” and “conjugated”
hyperbilirubinemia. Direct bilirubin assays measure conjugated plus some
unconjugated and delta bilirubin. Direct bilirubin reference intervals will vary
across hospitals, due to laboratory specifics including pH, temperature, and
reaction time. Conjugated bilirubin assays, on the other hand, measure only the
mono- and diconjugated forms of bilirubin using direct spectrophotometry.
Conjugated bilirubin assays have similar reference intervals across laboratories.
Thus, using the conjugated bilirubin level (if available) is more specific and
values are applicable across locations.
ETIOLOGIES
Once an elevated conjugated bilirubin value has been identified, the next step is
to consider the causes that explain the finding. A systematic approach to making
the diagnosis is helpful ( Fig. 44.1 ). The key decision point in the emergency
department is to identify those patients with evidence of liver failure. Any liver
failure requires ICU management for stabilization and further evaluation. Any
neonate with conjugated hyperbilirubinemia, even if not in liver failure, should be
admitted for further workup and most importantly to rule out biliary atresia (BA).
A stable, older child not in failure can most often be evaluated as an outpatient
after consultation with a pediatric gastroenterologist or hepatologist.
Conceptually, conjugated hyperbilirubinemia occurs for four reasons: elevation
from increased bilirubin production, hepatocyte injury, bilirubin transporter
defects, or obstruction.
Increased bilirubin production: When there is bilirubin overproduction, the
abundance of unconjugated bilirubin must be converted to conjugated bilirubin
in order for it to be excreted. As a result, conjugated bilirubin levels can rise. In
newborns, red blood cell lysis, ABO incompatibility, G6PD, and
cephalohematoma can all cause an abundance of unconjugated and
subsequently conjugated bilirubin.
Hepatocyte injury: Hepatocyte injury from any mechanism will cause the
breakdown of the liver cell, which results in the release of conjugated bilirubin
into the bloodstream. This occurs with liver failure, toxic injury, infections, and
metabolic disorders.
Bilirubin transporter defects: Transporter defects can be acquired in the
setting of general liver injury and prevent the normal passage of bile (including
conjugated bilirubin) out of the liver. Transporter defects can also be isolated
only to conjugated bilirubin transport, that is, Dubin–Johnson syndrome. In
these situations, conjugated bilirubin (but not other components of bile such as
toxic bile acids) is retained in the liver. This leads to liver discoloration but no
other liver toxicity.
Obstruction: When the biliary tree becomes obstructed, liver damage results.
The classic example is BA, where bile salts back up into the liver and induce
rapid fibrosis, cirrhosis, and eventual end-stage liver disease.
(See Table 44.1 .)
FIGURE 44.1 Approach to the patient with conjugated hyperbilirubinemia.
TABLE 44.1
CAUSES OF CONJUGATED HYPERBILIRUBINEMIA
Elevated production
• Sickle hemoglobinopathies
• ABO incompatibility
• G6PD deficiency
• Cephalohematoma
Hepatocyte injury
• Acute liver failure
• Hepatotoxins: drugs such as acetaminophen—see section Evaluation of the
Older Child
• TORCHS and perinatal/congenital infections
• Toxoplasmosis
• Rubella
• Cytomegalovirus
• Varicella zoster
• Herpes simplex virus
• Coxsackievirus
• Parvovirus B19
• Human immunodeficiency virus
• Syphilis
• Epstein–Barr virus
• Acquired infections
• Sepsis
• Urinary tract infection
• Metabolic disorders
• Galactosemia
• Galactokinase deficiency
• Hereditary fructose intolerance
• Genetic disorders
• α1 -Antitrypsin deficiency
• Wilson disease
• Autoimmune
• Autoimmune hepatitis
Transporter problem
• Sepsis
• Dubin–Johnson syndrome
