Question

Conjugated bilirubin is A. transported in blood bound to serum albumin. B. deficient in Crigler-Najjar syndrome, a deficiency of a UDPglucuronosyltransferase. C. reduced in serum in biliary tract obstruction. D. the form of bilirubin most elevated in hepatic (liver) disease. E. less soluble in aqueous solution than the unconjugated form.

Short answer

A) It is insoluble in water and binds to serum albumin for transport. B) Decreased levels may be seen in Crigler-Najjar syndrome. C) Its serum levels decrease in biliary tract obstruction. D) Hepatic disease can result in elevated levels. E) It is more soluble in aqueous solution compared to unconjugated bilirubin. Answer: B) Decreased levels may be seen in Crigler-Najjar syndrome.

Step-by-step solution

Understand the properties of bilirubin

Bilirubin, a by-product of heme metabolism, has two forms: conjugated and unconjugated. Unconjugated bilirubin is insoluble in water, while conjugated bilirubin is water-soluble. Unconjugated bilirubin binds with serum albumin to be transported to the liver, where it is conjugated with glucuronic acid. Conjugated bilirubin is then excreted from the liver into the bile ducts and then to the intestine, where it contributes to the formation of feces.

Analyze each option

A. Conjugated bilirubin is, by definition, soluble in water and does not need albumin for transport, and this option refers to unconjugated bilirubin. B. Crigler-Najjar syndrome is characterized by the deficiency of UDP-glucuronosyltransferase enzyme, which plays a role in the conjugation of bilirubin. So, the deficiency would lead to decreased conjugated bilirubin levels. C. Biliary tract obstruction would lead to reduced excretion of conjugated bilirubin into the bile ducts; hence, its level in serum would increase, not decrease. D. Hepatic (liver) disease would cause an elevation of both unconjugated and conjugated bilirubin levels, depending on the severity and nature of the damage. However, this statement does not specifically address conjugated bilirubin properties. E. Conjugated bilirubin is more soluble in aqueous solution as compared to unconjugated bilirubin, which is insoluble in water.

Choose the correct option

Based on the analysis of each option, Option B correctly describes conjugated bilirubin's involvement in Crigler-Najjar syndrome, and therefore, is the right choice.