Gastrointestinal physiology: conjugated hyperbilirubinaemia: practice question

A Physiology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Physiology · Gastrointestinal physiology: conjugated hyperbilirubinaemia

Sample item

A 20-year-old has mild recurrent jaundice with total bilirubin 4 mg/dL, more than half conjugated, dark urine, and normal ALT and alkaline phosphatase. Liver biopsy shows dark brown-black pigment in hepatocytes. Which defect is present?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Impaired canalicular excretion of conjugated bilirubin because of an MRP2 defect

Dubin-Johnson syndrome is due to an MRP2 (ABCC2) mutation that blocks canalicular export of conjugated bilirubin, causing a conjugated hyperbilirubinaemia, bilirubinuria and a black pigmented liver, with otherwise normal tests. Rotor syndrome has a similar biochemical picture but no pigment.

Option by option

  • A. Deficiency of UDP-glucuronosyltransferase 1A1

    UGT1A1 deficiency (Gilbert, Crigler-Najjar) gives unconjugated hyperbilirubinaemia with no bilirubinuria.

  • B. Impaired hepatocyte uptake of bilirubin through OATP transporters

    An uptake defect fits Rotor syndrome, in which the liver is not pigmented.

  • C. Impaired canalicular excretion of conjugated bilirubin because of an MRP2 defect (correct)

    Correct. Failed canalicular export with pigment accumulation is Dubin-Johnson syndrome.

  • D. Excessive haemolysis overwhelming conjugation

    Haemolysis gives mainly unconjugated hyperbilirubinaemia without a pigmented liver.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Impaired canalicular excretion of conjugated bilirubin because of an MRP2 defect. Dubin-Johnson syndrome is due to an MRP2 (ABCC2) mutation that blocks canalicular export of conjugated bilirubin, causing a conjugated hyperbilirubinaemia, bilirubinuria and a black pigmented liver, with otherwise normal tests.

Why is "Deficiency of UDP-glucuronosyltransferase 1A1" not the answer?

UGT1A1 deficiency (Gilbert, Crigler-Najjar) gives unconjugated hyperbilirubinaemia with no bilirubinuria.

Why is "Impaired hepatocyte uptake of bilirubin through OATP transporters" not the answer?

An uptake defect fits Rotor syndrome, in which the liver is not pigmented.

Why is "Excessive haemolysis overwhelming conjugation" not the answer?

Haemolysis gives mainly unconjugated hyperbilirubinaemia without a pigmented liver.

What concept does this question test?

It tests Gastrointestinal physiology: conjugated hyperbilirubinaemia in Physiology. Rotor syndrome has a similar biochemical picture but no pigment.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Gastrointestinal physiology: conjugated hyperbilirubinaemia?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.