Gastroenterology: lactose intolerance: practice question

A General Medicine 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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General Medicine · Gastroenterology: lactose intolerance

Sample item

A 22-year-old has bloating, flatulence and watery diarrhoea within an hour of drinking milk. Stool pH is acidic and reducing substances are positive. Which test best confirms the diagnosis?

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

The answer and the reasoning

B. Hydrogen breath test after a lactose load

Lactase deficiency leaves lactose unabsorbed, so colonic bacteria ferment it to gas and short-chain fatty acids, causing osmotic diarrhoea with an acidic stool. A raised breath hydrogen after a lactose load confirms malabsorption. Symptoms improve with a lactose-free diet.

Option by option

  • A. Stool examination for ova and cysts

    Stool ova and cysts look for parasites, which do not explain the milk relationship.

  • B. Hydrogen breath test after a lactose load (correct)

    Correct. Excess hydrogen after lactose ingestion proves lactose malabsorption.

  • C. Colonoscopy with biopsy

    Colonoscopy is not needed because the mucosa is normal.

  • D. Anti-tissue transglutaminase antibody

    Anti-tTG screens for coeliac disease, which is not suggested by milk-specific symptoms.

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 General Medicine question

What is the answer to this General Medicine question?

The best answer is B, Hydrogen breath test after a lactose load. Lactase deficiency leaves lactose unabsorbed, so colonic bacteria ferment it to gas and short-chain fatty acids, causing osmotic diarrhoea with an acidic stool.

Why is "Stool examination for ova and cysts" not the answer?

Stool ova and cysts look for parasites, which do not explain the milk relationship.

Why is "Colonoscopy with biopsy" not the answer?

Colonoscopy is not needed because the mucosa is normal.

Why is "Anti-tissue transglutaminase antibody" not the answer?

Anti-tTG screens for coeliac disease, which is not suggested by milk-specific symptoms.

What concept does this question test?

It tests Gastroenterology: lactose intolerance in General Medicine. A raised breath hydrogen after a lactose load confirms malabsorption. Symptoms improve with a lactose-free diet.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Gastroenterology: lactose intolerance?

For each disease know the classic presentation, the best test, and the first-line treatment. Then use the flashcards and the other General Medicine 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.