Schick test is for –
**Core Concept**
The Schick test is a method used to determine an individual's susceptibility to diphtheria, a bacterial infection caused by Corynebacterium diphtheriae. This test assesses the body's ability to mount an immune response against the diphtheria toxin.
**Why the Correct Answer is Right**
The Schick test involves injecting a small amount of diphtheria toxin into the skin, typically on the forearm. The response to the toxin is observed over the next 24-48 hours, and the test result is categorized as either positive (indicating susceptibility) or negative (indicating immunity). The test relies on the individual's existing immunity to the toxin, which is mediated by antibodies produced by the immune system. In individuals with active immunity, the antibodies neutralize the toxin, preventing a localized reaction at the injection site.
**Why Each Wrong Option is Incorrect**
**Option A:** The Mantoux test is a skin test used to assess an individual's immunity to tuberculosis, not diphtheria.
**Option B:** The Tuberculin test is another name for the Mantoux test, which is used to diagnose tuberculosis, not diphtheria.
**Option C:** The Widal test is a serological test used to diagnose typhoid fever, not diphtheria.
**Clinical Pearl / High-Yield Fact**
The Schick test is an important tool in public health, as it helps identify individuals who are susceptible to diphtheria and require vaccination. This test is particularly useful in areas with low vaccination rates or in individuals who have not been vaccinated.
**Correct Answer: D.**