Scratch test looks for what type of hypersensitivity reaction?

Scratch test looks for what type of hypersensitivity reaction?

• A. Type II
• B. Type III
• C. Type I
• D. Type IV

Answer: (C)

Scratch testing identifies immediate, IgE-mediated allergic responses, i.e., Type I hypersensitivity. If a person is sensitized to an allergen, the allergen cross-links IgE on mast cells in the skin, triggering degranulation and release of histamine and other mediators, producing a localized wheal-and-flare within about 15–20 minutes. This distinguishes Type I from other hypersensitivity types, which are either antibody-mediated cytotoxic (Type II), immune complex–mediated (Type III), or delayed-type T-cell–mediated (Type IV).

Scratch testing identifies immediate, IgE-mediated allergic responses, i.e., Type I hypersensitivity. If a person is sensitized to an allergen, the allergen cross-links IgE on mast cells in the skin, triggering degranulation and release of histamine and other mediators, producing a localized wheal-and-flare within about 15–20 minutes. This distinguishes Type I from other hypersensitivity types, which are either antibody-mediated cytotoxic (Type II), immune complex–mediated (Type III), or delayed-type T-cell–mediated (Type IV).