Sepsis biomarkers: procalcitonin: 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 · Sepsis biomarkers: procalcitonin

Sample item

A 30-year-old with fever and cough for 2 days has serum procalcitonin of 0.08 ng/mL. What does this suggest?

AFungal sepsis, because procalcitonin is low in bacterial infectionBSystemic bacterial infection is unlikely, so a viral or localised illness is more likelyCSevere bacterial sepsis with high probabilityDThe test is uninterpretable outside the neonatal period

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

The answer and the reasoning

B. Systemic bacterial infection is unlikely, so a viral or localised illness is more likely

Procalcitonin rises in response to bacterial infection, driven by cytokines and endotoxin, while interferon released during viral infection tends to suppress it. A very low level makes systemic bacterial infection unlikely, and serial values can help guide stopping antibiotics. It must be interpreted with the clinical picture.

Option by option

A. Fungal sepsis, because procalcitonin is low in bacterial infection
Procalcitonin is not a marker that rises in bacterial and falls in fungal infection in this way.
B. Systemic bacterial infection is unlikely, so a viral or localised illness is more likely (correct)
Correct. A low procalcitonin lowers the likelihood of systemic bacterial infection.
C. Severe bacterial sepsis with high probability
Sepsis is accompanied by markedly raised procalcitonin, not a low level.
D. The test is uninterpretable outside the neonatal period
The test is used in adults as well as neonates.

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 Microbiology question

What is the answer to this Microbiology question?

The best answer is B, Systemic bacterial infection is unlikely, so a viral or localised illness is more likely. Procalcitonin rises in response to bacterial infection, driven by cytokines and endotoxin, while interferon released during viral infection tends to suppress it.

Why is "Fungal sepsis, because procalcitonin is low in bacterial infection" not the answer?

Procalcitonin is not a marker that rises in bacterial and falls in fungal infection in this way.

Why is "Severe bacterial sepsis with high probability" not the answer?

Sepsis is accompanied by markedly raised procalcitonin, not a low level.

Why is "The test is uninterpretable outside the neonatal period" not the answer?

The test is used in adults as well as neonates.

What concept does this question test?

It tests Sepsis biomarkers: procalcitonin in Microbiology. A very low level makes systemic bacterial infection unlikely, and serial values can help guide stopping antibiotics. It must be interpreted with the clinical picture.

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 Sepsis biomarkers: procalcitonin?

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.