A 6-week-old infant is admitted to the hospital with jaundice. Her out-patient blood work demonstrated a total bilirubin of 12 mg/dL with a direct portion of 3.5 mg/dL. Which of the following disorders is most likely to be responsible?

Obstructive jaundice (ie, direct- reacting bilirubin greater than 20% of the total) requires investigation in all infants. CF and a1-antitrypsin deficiency should be considered in the diagnostic evaluation of any child with obstructive jaundice. Other diseases to be excluded are galactosemia, tyrosinemia, and urinary tract or other infections (including toxoplasmosis, cytomegalovirus, rubella, syphilis, and herpesvirus). Ultrasound examination to rule out choledochal cyst may be included with a 99mTc99 hepatic iminodiacetic acid (HIDA) scan to assess the patency of the biliary tree. Liver biopsy can assist in the diagnosis by providing a histologic diagnosis (eg, hepatitis, biliary atresia), tissue for enzyme activity (ie, inborn error of metabolism), or tissue for microscopic determination of storage diseases. ABO and Rh incompatibility occasionally cause direct hyperbilirubinemia if there were brisk hemolysis at birth, which would then lead to inspissated bile syndrome. All of the other causes listed typically lead to indirect hyperbilirubinemia.