Mycology: serum beta-D-glucan: practice question

A Microbiology 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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Microbiology · Mycology: serum beta-D-glucan

Sample item

A neutropenic patient with persistent fever is being screened with serum (1,3)-beta-D-glucan. Which of the following invasive infections would typically not raise this test despite being active?

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

The answer and the reasoning

A. Mucormycosis

Beta-D-glucan is a cell wall component of many fungi, including Candida, Aspergillus and Pneumocystis, so the serum assay is a broad screen for invasive fungal infection. Mucorales have little beta-D-glucan, and Cryptococcus is encapsulated, so these infections usually give a negative result. A negative test therefore does not exclude mucormycosis.

Option by option

  • A. Mucormycosis (correct)

    Mucorales contain little beta-D-glucan, so the assay is typically negative.

  • B. Invasive aspergillosis

    Aspergillus releases glucan and the test is positive in invasive disease.

  • C. Invasive candidiasis

    Candida has glucan in its wall and invasive candidiasis commonly raises the test.

  • D. Pneumocystis jirovecii pneumonia

    Pneumocystis gives very high glucan values and the test is used to support the diagnosis.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Mucormycosis. Beta-D-glucan is a cell wall component of many fungi, including Candida, Aspergillus and Pneumocystis, so the serum assay is a broad screen for invasive fungal infection.

Why is "Invasive aspergillosis" not the answer?

Aspergillus releases glucan and the test is positive in invasive disease.

Why is "Invasive candidiasis" not the answer?

Candida has glucan in its wall and invasive candidiasis commonly raises the test.

Why is "Pneumocystis jirovecii pneumonia" not the answer?

Pneumocystis gives very high glucan values and the test is used to support the diagnosis.

What concept does this question test?

It tests Mycology: serum beta-D-glucan in Microbiology. Mucorales have little beta-D-glucan, and Cryptococcus is encapsulated, so these infections usually give a negative result. A negative test therefore does not exclude mucormycosis.

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 Mycology: serum beta-D-glucan?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.