WBR0494
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Immunology |
| Sub Category | SubCategory::Endocrine |
| Prompt | [[Prompt::A 27-year-old newly graduate nurse applied for a job at a hospital. As part of her pre-employment screening tests, she had to submit a copy of her vaccination history as well as to undergo a ppd test to screen for tuberculosis. The patient received an intradermal injection of ppd and was asked to come back again after 48 hours to reevaluate the site of injection. Which of the following mechanisms would be involved if the patient returned 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. PPD skin test is not a type I hypersensitivity disorder.]] |
| 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. 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. PPD skin test is not a type III hypersensitivity order. |
| 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, 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::B |
| Explanation | [[Explanation::PPD test, also known as the Mantoux test, tuberculin sensitivity test, Pirquet test, is a screening tool for tuberculosis. The results of this test must be interpreted carefully. The person's medical risk factors determine at which increment (5 mm, 10 mm, or 15 mm) of induration the result is considered positive. PPD test is characterized by delayed T-cell mediated immune reactions and hence it is a type IV hypersensitivity immune reaction.
Educational Objective:
Hypersensitivity type IV disorders include conditions characterized by delayed T-cell mediated immune reactions such as contact dermatitis, PPD testing. |
| Approved | Approved::No |
| Keyword | WBRKeyword::Hypersensitivity, WBRKeyword::PPD test |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |