Gastrointestinal: D-xylose absorption test: 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: D-xylose absorption test

Sample item

In a patient with chronic diarrhoea and steatorrhoea, the oral D-xylose absorption test is abnormal. What does this indicate?

AIsolated lactase deficiencyBPancreatic exocrine insufficiencyCDisease of the small intestinal mucosa, as in coeliac diseaseDBile salt deficiency

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

The answer and the reasoning

C. Disease of the small intestinal mucosa, as in coeliac disease

D-xylose is a pentose absorbed passively across healthy proximal small bowel mucosa and does not need pancreatic enzymes or bile. A low urinary excretion therefore points to mucosal disease, whereas the test is normal in pancreatic steatorrhoea.

Option by option

A. Isolated lactase deficiency
Lactase deficiency affects lactose digestion, not xylose absorption.
B. Pancreatic exocrine insufficiency
In pancreatic insufficiency the test is normal because no digestion is needed.
C. Disease of the small intestinal mucosa, as in coeliac disease (correct)
Correct. The test depends only on intact mucosa, so a low result indicates mucosal disease.
D. Bile salt deficiency
Bile salt deficiency does not alter D-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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, Disease of the small intestinal mucosa, as in coeliac disease. D-xylose is a pentose absorbed passively across healthy proximal small bowel mucosa and does not need pancreatic enzymes or bile.

Why is "Isolated lactase deficiency" not the answer?

Lactase deficiency affects lactose digestion, not xylose absorption.

Why is "Pancreatic exocrine insufficiency" not the answer?

In pancreatic insufficiency the test is normal because no digestion is needed.

Why is "Bile salt deficiency" not the answer?

Bile salt deficiency does not alter D-xylose absorption.

What concept does this question test?

It tests Gastrointestinal: D-xylose absorption test in Physiology. A low urinary excretion therefore points to mucosal disease, whereas the test is normal in pancreatic steatorrhoea.

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: D-xylose absorption test?

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.