## **Core Concept**
Hepatitis B virus (HBV) infection involves various serological markers that help in understanding the phase of infection. The active replication of HBV is a critical phase where the virus is actively multiplying in the liver.

## **Why the Correct Answer is Right**
The correct answer, **HBeAg (Hepatitis B e-antigen)**, indicates active viral replication. HBeAg is a marker of HBV replication and high infectivity. When HBV is actively replicating, it produces HBeAg, which is secreted into the bloodstream. The presence of HBeAg suggests that the virus is actively replicating in the liver and the patient is highly infectious.

## **Why Each Wrong Option is Incorrect**
* **Option A: Anti-HBc (Antibody to Hepatitis B core antigen)** - This is a marker of current or past HBV infection but does not specifically indicate active replication.
* **Option B: HBsAg (Hepatitis B surface antigen)** - While HBsAg indicates current infection, it does not specifically denote active replication; it can be present in both replicative and non-replicative phases.
* **Option D: Anti-HBe (Antibody to Hepatitis B e-antigen)** - This indicates a response to HBeAg and typically signifies a transition to a less active or inactive carrier state, suggesting lower viral replication.

## **Clinical Pearl / High-Yield Fact**
A crucial clinical pearl is that the presence of **HBeAg** along with **HBsAg** and high HBV DNA levels confirms active viral replication. This phase is associated with a higher risk of liver inflammation, fibrosis progression, and transmission to others.

## **Correct Answer:** . HBeAg.