What is the first sign of hepatitis B infection?

The presence of HBsAg (Hepatitis B surface antigen) is the first sign of hepatitis B infection. HBsAg is a protein on the surface of the hepatitis B virus that can be detected in the serum during an active infection. This antigen is typically the first serological marker to appear after exposure to the virus, signaling that the body is currently hosting an infection. The presence of this antigen confirms that the person is infected with hepatitis B, whether acutely or chronically.

While IgM antibodies can indicate an acute infection, they appear later in the course of the disease compared to HBsAg. Detection of anti-HBc (antibody to hepatitis B core antigen) typically signifies a past or ongoing infection, and anti-HBs (antibody to HBsAg) indicates recovery or vaccination against hepatitis B, emerging only after clearance of HBsAg. This serological sequence establishes the significance of HBsAg as the primary indicator of active infection.