WBR0494

Author	[[PageAuthor::Rim Halaby, M.D. [1], Alison Leibowitz [2] (Reviewed by Alison Leibowitz)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Immunology
Sub Category	SubCategory::Endocrine
Prompt	[[Prompt::A 27-year-old newly graduated nurse applying for a job at a hospital has to submit a copy of her vaccination history and undergo a PPD test, to screen for tuberculosis. She receives an intradermal injection of PPD and is asked to return 48 hours later, so that site of injection can be reevaluated. Which of the following mechanisms is involved if the female returns with an induration at the site of the PPD injection?]]
Answer A	AnswerA::Hypersensitivity type I
Answer A Explanation	[[AnswerAExp::Type I hypersensitivity disorders include anaphylaxis, atopy, and allergy. A PPD skin test is not a type I hypersensitivity immune reaction.]]
Answer B	AnswerB::Hypersensitivity type II
Answer B Explanation	AnswerBExp::Type II hypersensitivity disorders include conditions where an antibody is directed against a specific antigen. A PPD skin test involves a delayed T cell mediated response that is consistent with type IV hypersensitivity.
Answer C	AnswerC::Hypersensitivity type III
Answer C Explanation	AnswerCExp::Hypersensitivity type III disorders include conditions where an antigen-antibody complex forms and activates the complement system. A PPD skin test is not a type III hypersensitivity immune reaction.
Answer D	AnswerD::Hypersensitivity type IV
Answer D Explanation	[[AnswerDExp::Hypersensitivity type IV disorders include conditions characterized by delayed T-cell mediated immune reactions, such as contact dermatitis and tuberculosis testing.]]
Answer E	AnswerE::Not a hypersensitivity disorder
Answer E Explanation	AnswerEExp::PPD skin test is a type IV hypersensitivity disorder.
Right Answer	RightAnswer::D
Explanation	[[Explanation::PPD test, also known as the Mantoux test, tuberculin sensitivity test, and Pirquet test, is a screening tool for tuberculosis. The individual's medical risk factors determine the increment (5 mm, 10 mm, or 15 mm) of induration at which the result is considered positive. A PPD test, a type IV hypersensitivity immune reaction, is characterized by delayed T-cell mediated immune reactions. Educational Objective: Hypersensitivity type IV disorders include conditions characterized by delayed T-cell mediated immune reactions, such as contact dermatitis and PPD testing. References: First Aid 2014 page 208]]
Approved	Approved::Yes
Keyword	WBRKeyword::Hypersensitivity, WBRKeyword::PPD test, WBRKeyword::immune system, WBRKeyword::testing, WBRKeyword::TB, WBRKeyword::tuberculosis, WBRKeyword::screening
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::