Positive Shick’s test indicates that the person is
So, first, I need to recall what the Shick test actually measures. From what I remember, the Shick test is used to determine if a person is susceptible to diphtheria. It involves injecting a small amount of diphtheria toxin and seeing if there's a reaction. If there's a reaction, that means the person doesn't have sufficient antibodies to neutralize the toxin, hence they are susceptible.
Wait, so a positive Shick's test means the person is susceptible because they don't have immunity. Conversely, a negative test would mean they have immunity, either from vaccination or prior infection. Let me double-check that. Yes, the Shick test is based on the principle that a person with antibodies against diphtheria toxin will not react to a small dose of the toxin. If they do react, they lack those antibodies and are therefore susceptible.
Now, looking at the options. The correct answer here is that a positive Shick test indicates susceptibility. The other options might be things like immunity, previous infection, or vaccination status. For example, if someone is vaccinated, they would have antibodies and the test would be negative. So the incorrect options would be the opposite. Let me structure each part of the explanation accordingly.
Core Concept: The Shick test assesses susceptibility to diphtheria by detecting the presence of protective antibodies. It's a skin test using diphtheria toxin.
Why Correct Answer is Right: A positive result means the person lacks sufficient antibodies, so they're not immune. The test works by observing a local reaction (redness, swelling) indicating the body can't neutralize the toxin.
Incorrect Options: If an option says "immune" or "vaccinated," that's wrong because a positive test shows lack of immunity. Another might be "has had diphtheria," but that's also incorrect since prior infection usually gives immunity, leading to a negative test.
Clinical Pearl: Remember that a positive Shick test means no immunity—so vaccination is needed. The test is less commonly used now due to widespread vaccination programs.
Make sure the answer is concise and fits within the character limit. Check each section for clarity and accuracy.
**Core Concept**
The Shick test evaluates susceptibility to **diphtheria** by detecting the presence of **antidiphtheria antibodies**. A positive result indicates **lack of immunity**, while a negative result suggests prior vaccination or natural immunity.
**Why the Correct Answer is Right**
A positive Shick test occurs when **no neutralizing antibodies** are present to counteract the injected diphtheria toxin. This leads to a localized inflammatory reaction (redness, swelling) within 24–48 hours, confirming **susceptibility to diphtheria**. The test is based on the principle that **antibodies against diphtheria toxin** (produced via vaccination or prior infection) prevent toxin-mediated cell damage.
**Why Each Wrong Option is Incorrect**
**Option A:** *Immune to diphtheria* – Incorrect. A positive test indicates **lack of immunity**; immune individuals would show no reaction.
**Option