What does HBsAg testing reveal?

HBsAg testing reveals the presence of the hepatitis B virus (HBV) in a person's blood. This antigen is a surface protein of the virus that indicates an active infection. When a laboratory test returns positive for HBsAg, it means that the individual is currently infected with hepatitis B, whether it be acute or chronic.

The importance of detecting HBsAg lies in its role as an early marker of hepatitis B infection. A positive result suggests that the virus is replicating in the individual, which can lead to liver inflammation and other complications. This finding is crucial for diagnosing hepatitis B and for determining appropriate management and treatment options.

In the context of the other choices, immunity to hepatitis B (as mentioned in the first choice) would be indicated by the presence of antibodies to HBsAg rather than the antigen itself. Previous infection with hepatitis C is unrelated to HBsAg since this antigen pertains specifically to hepatitis B. Lastly, a negative result for all hepatitis types is also not applicable, as HBsAg solely indicates hepatitis B infection and does not account for tests related to other hepatitis viruses.