In a patient only Anti HBsAg is positive in serum, all other viral markers are negative. This indicates
**Core Concept**
The presence of anti-HBsAg (antibody to hepatitis B surface antigen) in a patient's serum, without any other viral markers, suggests a specific immunological response to a hepatitis B virus (HBV) infection. This indicates that the patient has developed immunity to HBV, either through vaccination or past infection.
**Why the Correct Answer is Right**
When a patient is infected with HBV, their body mounts an immune response, producing antibodies against the surface antigen (HBsAg) of the virus. In individuals who have been vaccinated against HBV, anti-HBsAg is present due to the introduction of HBsAg from the vaccine, which stimulates the production of antibodies. In patients who have recovered from an HBV infection, anti-HBsAg is also present, indicating a successful immune response and immunity to future infections. This immune response is specific to the surface antigen and does not affect other viral markers.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the presence of anti-HBsAg alone does not indicate acute HBV infection, which is typically characterized by the presence of HBsAg and other viral markers.
**Option B:** This option is incorrect because the absence of anti-HBc (antibody to hepatitis B core antigen) suggests that the patient has not been infected with HBV in the past, making it unlikely that they have developed immunity through past infection.
**Option C:** This option is incorrect because the presence of anti-HBsAg does not indicate a chronic HBV infection, which is typically characterized by the presence of HBsAg and other viral markers.
**Clinical Pearl / High-Yield Fact**
It is essential to note that the presence of anti-HBsAg can also be seen in individuals who have been vaccinated against HBV, making it crucial to consider the patient's vaccination history when interpreting serological results.
**Correct Answer: B. This indicates immunity due to past infection or vaccination.**