Immunology: anaphylaxis tryptase: 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 · Immunology: anaphylaxis tryptase

Sample item

A 34-year-old woman collapses 20 minutes after a wasp sting with urticaria, wheeze and hypotension, and recovers after intramuscular adrenaline. The allergist wants laboratory support for the diagnosis of anaphylaxis. Which test is most appropriate, and when should the sample be taken?

ATotal serum IgE, taken at any timeBSerum mast cell tryptase, taken within about 1 to 3 hours of onsetCSerum histamine, taken 6 hours after onsetDSerum C3 level, taken 24 hours after onset

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

The answer and the reasoning

B. Serum mast cell tryptase, taken within about 1 to 3 hours of onset

Tryptase is released from mast cell granules, peaks about 1 to 2 hours after the reaction and falls slowly, with a half-life of roughly 2 hours. A value above the patient's baseline supports mast cell degranulation. Histamine is cleared within minutes, so it is of little use.

Option by option

A. Total serum IgE, taken at any time
Total IgE reflects atopic status and does not confirm that an acute reaction occurred.
B. Serum mast cell tryptase, taken within about 1 to 3 hours of onset (correct)
Tryptase persists long enough in blood to be measured after the acute treatment, so a sample in this window is the standard confirmatory test.
C. Serum histamine, taken 6 hours after onset
Histamine is metabolised within minutes and would be normal by 6 hours.
D. Serum C3 level, taken 24 hours after onset
Complement consumption is not a feature of IgE-mediated anaphylaxis, and a level at 24 hours does not confirm it.

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, Serum mast cell tryptase, taken within about 1 to 3 hours of onset. Tryptase is released from mast cell granules, peaks about 1 to 2 hours after the reaction and falls slowly, with a half-life of roughly 2 hours.

Why is "Total serum IgE, taken at any time" not the answer?

Total IgE reflects atopic status and does not confirm that an acute reaction occurred.

Why is "Serum histamine, taken 6 hours after onset" not the answer?

Histamine is metabolised within minutes and would be normal by 6 hours.

Why is "Serum C3 level, taken 24 hours after onset" not the answer?

Complement consumption is not a feature of IgE-mediated anaphylaxis, and a level at 24 hours does not confirm it.

What concept does this question test?

It tests Immunology: anaphylaxis tryptase in Microbiology. A value above the patient's baseline supports mast cell degranulation. Histamine is cleared within minutes, so it is of little use.

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 Immunology: anaphylaxis tryptase?

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.