Which condition would result in elevations in primarily conjugated bilirubin?

• A. Dubin-Johnson syndrome
• B. Physiologic jaundice of the newborn
• C. Crigler-Najjar syndrome
• D. Gilbert's syndrome

Answer: (A)

Elevations in bilirubin that are primarily conjugated point to a problem with moving the already-conjugated bilirubin from the liver into the bile, rather than with making bilirubin in the first place. In Dubin-Johnson syndrome, a defect in the canalicular transporter that exports conjugated bilirubin into bile (MRP2) means that bilirubin diglucuronide can’t be efficiently excreted into the bile and instead leaks back into the bloodstream. The result is a predominantly direct (conjugated) hyperbilirubinemia, often mild and chronic, with a darkly pigmented liver on exam or biopsy. By contrast, conditions like physiologic jaundice of the newborn, Crigler-Najjar syndrome, and Gilbert’s syndrome mainly affect bilirubin processing before excretion, leading to elevated unconjugated bilirubin.