**Question:** Early diagnosis of acute hepatitis-B infection is made by

A. HBsAg (hepatitis B surface antigen)
B. HBeAg (hepatitis B e antigen)
C. HBV DNA PCR (hepatitis B virus DNA polymerase chain reaction)
D. HBsAb (hepatitis B surface antibody)

**Correct Answer:** A. HBsAg (hepatitis B surface antigen)

**Core Concept:** Early diagnosis of acute hepatitis-B infection relies on identifying specific markers of the virus in the patient's blood. Hepatitis B virus (HBV) has four main surface antigens (proteins produced by the virus): HBsAg, HBeAg, HBcAg (hepatitis B core antigen), and HBsAb (antibody to HBsAg).

**Why the Correct Answer is Right:** HBsAg is the key marker for acute hepatitis-B infection. It is present in the blood of infected individuals during the early stage of infection, typically within 1-3 months post-exposure. The detection of HBsAg indicates the presence of the virus and active infection.

**Why Each Wrong Option is Incorrect:**

**A. HBsAg:** As mentioned above, HBsAg is essential for diagnosing acute hepatitis-B infection.

**B. HBeAg:** Hepatitis B e antigen (HBeAg) is present in the blood during the early phase of infection but is not specific for acute hepatitis-B infection. HBeAg is also found in chronic hepatitis B infection, which is more common than acute hepatitis-B infection.

**C. HBV DNA PCR:** Polymerase chain reaction (PCR) is a molecular technique used to amplify and detect specific genetic material (DNA) from a sample. HBV DNA PCR is essential for diagnosing chronic hepatitis B infection, but it is not specific for acute hepatitis-B infection. The presence of HBV DNA PCR alone does not confirm acute infection.

**D. HBsAb:** Anti-HBsAg (HBsAb) is the antibody to HBsAg and develops in response to previous HBsAg exposure, indicating past infection or vaccination. It is not useful for diagnosing acute hepatitis-B infection.

**Core Concept:** Early diagnosis of acute hepatitis-B infection relies on identifying the presence of HBsAg, which indicates active infection.

**Why Each Wrong Option is Incorrect:**

HBeAg, HBV DNA PCR, and HBsAb are not specific for acute hepatitis-B infection and should be used in conjunction with HBsAg rather than as alternatives.

**Clinical Pearls:**

1. Early diagnosis of acute hepatitis-B infection is essential for initiating appropriate treatment and preventing transmission to others.
2. Combining HBsAg, HBeAg, HBV DNA PCR, and anti-HBs (HBsAb) testing can provide a more accurate diagnosis of acute hepatitis-B infection.
3. HBsAg is crucial for diagnosing acute hepatitis-B infection as it indicates active viral replication and presence of the virus in the bloodstream.
4. HBeAg, HBV DNA PCR, and anti-H