Immunology: skin prick test reading: 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.

Try it

Microbiology · Immunology: skin prick test reading

Sample item

A 14-year-old with seasonal sneezing has a skin prick test performed with a drop of grass pollen extract, and a wheal with surrounding flare develops. When is this reaction normally read, and what mediates it?

AAfter 48 to 72 hours; sensitised T cellsBAfter 6 to 8 hours; complement and neutrophilsCAfter 15 to 20 minutes; histamine from IgE-sensitised mast cellsDAfter 2 weeks; antibody-antigen complexes

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

The answer and the reasoning

C. After 15 to 20 minutes; histamine from IgE-sensitised mast cells

The skin prick test detects type I hypersensitivity. Allergen cross-links specific IgE on dermal mast cells, which release histamine, and the wheal and flare appear within 15 to 20 minutes. Delayed reactions of 48 to 72 hours are type IV, as in the tuberculin and patch tests.

Option by option

A. After 48 to 72 hours; sensitised T cells
Reading at 48 to 72 hours with T cells describes delayed-type reactions such as the tuberculin test.
B. After 6 to 8 hours; complement and neutrophils
A 6 to 8 hour reaction describes the late-phase response, which follows the immediate wheal and is not the reading time of the prick test.
C. After 15 to 20 minutes; histamine from IgE-sensitised mast cells (correct)
Correct. A prompt wheal and flare reflects histamine release from IgE-bound mast cells.
D. After 2 weeks; antibody-antigen complexes
A reaction peaking in weeks with immune complexes resembles serum sickness, not a skin prick.

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 C, After 15 to 20 minutes; histamine from IgE-sensitised mast cells. The skin prick test detects type I hypersensitivity.

Why is "After 48 to 72 hours; sensitised T cells" not the answer?

Reading at 48 to 72 hours with T cells describes delayed-type reactions such as the tuberculin test.

Why is "After 6 to 8 hours; complement and neutrophils" not the answer?

A 6 to 8 hour reaction describes the late-phase response, which follows the immediate wheal and is not the reading time of the prick test.

Why is "After 2 weeks; antibody-antigen complexes" not the answer?

A reaction peaking in weeks with immune complexes resembles serum sickness, not a skin prick.

What concept does this question test?

It tests Immunology: skin prick test reading in Microbiology. Allergen cross-links specific IgE on dermal mast cells, which release histamine, and the wheal and flare appear within 15 to 20 minutes. Delayed reactions of 48 to 72 hours are type IV, as in the tuberculin and patch tests.

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: skin prick test reading?

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.