Hypersensitivity: type IV and patch testing: practice question

A Pathology 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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Pathology · Hypersensitivity: type IV and patch testing

Sample item

A 28-year-old woman has an itchy eczematous rash on her earlobes and under her jeans button that appeared two days after wearing new jewellery. Which test is used to confirm the causative allergen?

ADirect immunofluorescence of lesional skinBPatch test, read at 48 and 72 hoursCSerum allergen-specific IgE assayDSkin prick test, read at 15 to 20 minutes

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

The answer and the reasoning

B. Patch test, read at 48 and 72 hours

Nickel allergic contact dermatitis is a delayed type IV hypersensitivity, in which hapten-modified skin proteins sensitise T cells and re-exposure produces eczema after 24 to 72 hours. The investigation of choice is patch testing, in which allergens are applied under occlusion for 48 hours and read at 48 and 72 hours.

Option by option

A. Direct immunofluorescence of lesional skin
Direct immunofluorescence is used for blistering autoimmune disorders, not allergen identification.
B. Patch test, read at 48 and 72 hours (correct)
Correct. Patch testing detects delayed T-cell mediated contact allergy.
C. Serum allergen-specific IgE assay
Specific IgE assays measure type I sensitisation and are not helpful in contact dermatitis.
D. Skin prick test, read at 15 to 20 minutes
Prick testing detects immediate IgE mediated sensitisation, not contact dermatitis.

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 Pathology question

What is the answer to this Pathology question?

The best answer is B, Patch test, read at 48 and 72 hours. Nickel allergic contact dermatitis is a delayed type IV hypersensitivity, in which hapten-modified skin proteins sensitise T cells and re-exposure produces eczema after 24 to 72 hours.

Why is "Direct immunofluorescence of lesional skin" not the answer?

Direct immunofluorescence is used for blistering autoimmune disorders, not allergen identification.

Why is "Serum allergen-specific IgE assay" not the answer?

Specific IgE assays measure type I sensitisation and are not helpful in contact dermatitis.

Why is "Skin prick test, read at 15 to 20 minutes" not the answer?

Prick testing detects immediate IgE mediated sensitisation, not contact dermatitis.

What concept does this question test?

It tests Hypersensitivity: type IV and patch testing in Pathology. The investigation of choice is patch testing, in which allergens are applied under occlusion for 48 hours and read at 48 and 72 hours.

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 Hypersensitivity: type IV and patch testing?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.