Lipid metabolism: D-xylose absorption test: practice question

A Biochemistry 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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Biochemistry · Lipid metabolism: D-xylose absorption test

Sample item

A patient with steatorrhoea and normal renal function drinks 25 g of D-xylose, and urinary excretion over five hours is markedly reduced. Which cause of steatorrhoea is the most likely?

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

The answer and the reasoning

A. Coeliac disease with small intestinal mucosal damage

D-xylose is a pentose absorbed passively by the small intestinal mucosa without need for digestion or bile. Low urinary excretion with normal renal function points to mucosal disease such as coeliac disease. In pancreatic or biliary causes of steatorrhoea the mucosa is normal and xylose excretion is normal.

Option by option

  • A. Coeliac disease with small intestinal mucosal damage (correct)

    Correct. Reduced xylose excretion reflects a diseased absorptive mucosa.

  • B. Chronic pancreatitis

    Chronic pancreatitis causes maldigestion, and xylose needs no pancreatic enzymes, so excretion is normal.

  • C. Obstructive jaundice from carcinoma of the head of pancreas

    Biliary obstruction impairs fat absorption through bile salt loss, and xylose absorption is normal.

  • D. Orlistat therapy

    Orlistat blocks lipase in the gut lumen and does not impair xylose absorption.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is A, Coeliac disease with small intestinal mucosal damage. D-xylose is a pentose absorbed passively by the small intestinal mucosa without need for digestion or bile.

Why is "Chronic pancreatitis" not the answer?

Chronic pancreatitis causes maldigestion, and xylose needs no pancreatic enzymes, so excretion is normal.

Why is "Obstructive jaundice from carcinoma of the head of pancreas" not the answer?

Biliary obstruction impairs fat absorption through bile salt loss, and xylose absorption is normal.

Why is "Orlistat therapy" not the answer?

Orlistat blocks lipase in the gut lumen and does not impair xylose absorption.

What concept does this question test?

It tests Lipid metabolism: D-xylose absorption test in Biochemistry. Low urinary excretion with normal renal function points to mucosal disease such as coeliac disease. In pancreatic or biliary causes of steatorrhoea the mucosa is normal and xylose excretion is normal.

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 Lipid metabolism: D-xylose absorption test?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.