Genetics: cystic fibrosis diagnosis: practice question

A Pediatrics 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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Pediatrics · Genetics: cystic fibrosis diagnosis

Sample item

A 1-year-old with recurrent chest infections, steatorrhoea and failure to thrive is suspected to have cystic fibrosis. Which test is the standard diagnostic?

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

The answer and the reasoning

C. Sweat chloride above 60 mmol/L on pilocarpine iontophoresis

A sweat chloride level of 60 mmol/L or higher on two occasions confirms cystic fibrosis, caused by CFTR mutations, with the commonest being delta F508. Pancreatic insufficiency causes fatty stools. Genetic testing and immunoreactive trypsinogen are used for screening.

Option by option

  • A. Chest X-ray

    Chest X-ray shows nonspecific changes.

  • B. Stool culture

    Stool culture does not confirm CF.

  • C. Sweat chloride above 60 mmol/L on pilocarpine iontophoresis (correct)

    Correct. Sweat chloride above 60 mmol/L is diagnostic.

  • D. Serum amylase

    Amylase does not diagnose CF.

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 Pediatrics question

What is the answer to this Pediatrics question?

The best answer is C, Sweat chloride above 60 mmol/L on pilocarpine iontophoresis. A sweat chloride level of 60 mmol/L or higher on two occasions confirms cystic fibrosis, caused by CFTR mutations, with the commonest being delta F508.

Why is "Chest X-ray" not the answer?

Chest X-ray shows nonspecific changes.

Why is "Stool culture" not the answer?

Stool culture does not confirm CF.

Why is "Serum amylase" not the answer?

Amylase does not diagnose CF.

What concept does this question test?

It tests Genetics: cystic fibrosis diagnosis in Pediatrics. Pancreatic insufficiency causes fatty stools. Genetic testing and immunoreactive trypsinogen are used for screening.

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 Genetics: cystic fibrosis diagnosis?

Memorise milestones and the vaccine schedule as tables and revise them often. Then use the flashcards and the other Pediatrics 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.