The following is a marker of acute hepatitis B infection –
**Core Concept**
Acute hepatitis B infection is characterized by the presence of viral markers in the blood, which indicate active replication of the virus. The most commonly used markers include HBsAg (hepatitis B surface antigen), HBeAg (hepatitis B e-antigen), and anti-HBc IgM (immunoglobulin M antibody to hepatitis B core antigen). These markers are essential for diagnosing and managing acute hepatitis B infection.
**Why the Correct Answer is Right**
The correct answer is HBsAg. HBsAg is the first marker to appear in the blood after infection, typically 1-4 weeks before the onset of symptoms. It is present in 95-100% of patients with acute hepatitis B infection and remains detectable until the virus is cleared or the patient develops chronic infection. The presence of HBsAg indicates active viral replication and is associated with increased infectivity.
**Why Each Wrong Option is Incorrect**
**Option A:** HBeAg is a marker of viral replication, but it appears after HBsAg and is not a specific marker for acute infection.
**Option B:** Anti-HBc IgM is a marker of acute infection, but it appears later than HBsAg and is not as sensitive.
**Option C:** Anti-HBs (antibody to hepatitis B surface antigen) is a marker of immunity, either from vaccination or past infection, and is not a specific marker for acute infection.
**Clinical Pearl / High-Yield Fact**
Remember that HBsAg is a sensitive marker for acute hepatitis B infection, but it may also be present in patients with chronic infection or those who have recovered from acute infection. Always consider the clinical context and other laboratory results when interpreting HBsAg results.
**Correct Answer: B. Anti-HBc IgM.**